Category: Biodiversity Net Gain

Where does our lost habitat go?

Biodiversity net gain is moving habitat out of towns — but small sites are not the reason why

Two years into mandatory biodiversity net gain, a question worth asking is no longer whether developments are delivering at least 10% BNG — almost all of them do, on paper. The question to ask is: where does the biodiversity go answer what Parliament intended it to go?

Our earlier July blog — When a city builds, where does nature go? — asked where the compensating habitat goes physically, and found it travels a median 36 kilometres from where it was lost, and to less deprived places — this remains true today.

Note: These two blogs analyse their data differently — using a different classification of authorities, and 357 gain plans rather than 202 available in July — so figures should not be read across from one to the other. Where they appear to disagree, the note at the end explains why.

This blog asks a different question: how much habitat moves away, and do small development sites explain this?

We’ve been collecting evidence from the following sources:

  • 357 biodiversity gain plans downloaded from 38 local planning authorities’ planning portals and their FoI responses
  • the Biodiversity Gain Sites register (BGS register) as of 19 August 2026 — 2,328 developments and 2,686allocations.

We’ve also analysed the published statutory metric calculations, which give measured site areas for 202 of the plans.

We set out two findings that only appear when these datasets are looked at together. They are as follows:

Urban England is a net exporter of habitat units, at scale

The BGS register records, for every development that bought off-site units, whether the gain site sits within the same authority, in a neighbouring one, or somewhere else. We’ve classified each authority by its ONS 2021 Rural Urban Classification. The pattern is stark.

Table 1: Area habitat units. ‘Units required’ is what developments in that authority had to buy off-site; ‘Units hosted’ is what gain sites in that authority delivered to developments anywhere. London boroughs are a subset of Urban, not an additional row.

Nine in ten developments in Office of National Statistics (ONS)-defined urban authorities compensate outside their own area. In London it is 98.2% — of 113 developments on the BGS, two compensated at home. Urban authorities between them need 1,435 area units and host 602: a net outflow of 833 units of habitat from towns and cities to the countryside. What that means on the ground: at 192 Beech Hall Road in Waltham Forest, two new houses buy their 0.07 units from a habitat bank at Puddington in Mid Devon — 267 kilometres away — and deliver nothing at all on site. Section 6 of their gain plan, the section that records on-site enhancement, is blank.

Both rural classes are net importers on average, but the averages conceal a very wide spread. For example, the largest single importer is Barnsley (an ONS urban authority) which hosts 101.7 units against the 3.3 its own developments require. At the other end, Cherwell (an ONS Intermediate urban authority) needs 76.2 units and hosts 0.95, Westmorland and Furness (an ONS Intermediate rural authority) requires 61.2 but hosts nothing, while Manchester (an ONS urban authority) needs 48.6 but hosts nothing. What determines whether an authority imports or exports is not how urban it is, but whether anyone has registered a habitat bank inside it.

Note what the table does not show. There is no clean four-step gradient from urban to rural: Intermediate rural (59.3%) sits slightly below Majority rural (61.7%). The gradient is in fact two-step: strongly urban authorities export almost everything; for everywhere else the figure sits at around 60%.

Site size doesn’t explain it

The obvious explanation is that urban sites are cramped. A development on a small plot has nowhere to put lost habitat, so it buys it elsewhere. If that were right, the export pattern would be a led by size rather than policy, but this is not what happens.

Taking the 202 plans for which we hold a measured site area, we can see that between 40% and 47% of measured sites are at or below 0.2 hectares across every ONS class, with the median site between 0.21 and 0.28 hectares, whether the authority is Manchester or mid-Devon. The overall median is 0.243 hectares; a quarter of all sites are below 0.102 ha.

Table 1: Small sites are everywhere.

Nor do small sites drive habitat off site. Of the 90 sites at or below 0.2 hectares, 34% use off-site compensation (off-site or both — question 4.6 of the required Biodiversity Gain Plan). Of the 112 larger sites, 42% do. The relationship runs, weakly, the wrong way for the cramped-site theory.So the export of habitat from towns is not a consequence of urban plots being small. It is a consequence of where the available habitat banks are — and they are in the countryside, because that is where land is both cheaper and available. The spatial risk multiplier is meant to discourage distant compensation. On this evidence it is not discouraging it much.

What small sites actually deliver

The small-site analysis is worth reporting in its own right, because percentage compliance conceals what’s happening in absolute terms.

Table 1: Small-site analysis

Small sites are 45% of all measured sites but only 6.6% of the baseline biodiversity. Their median pre-development value is 0.170 biodiversity units — so the minimum statutory 10% BNG required amounts to 0.017 of a unit, equivalent to an area of improved habitat you could easily step across.

They meet the target as reliably as anyone: median on-site net change is +11.5% on small sites against +11.8% on larger ones. That equivalence is the point.

But percentage is not a quantity. Two developments can both report ‘12% net gain’ while one creates a meadow and the other creates a planter, and the 10% BNG test cannot tell them apart.

This matters most in towns, because that is where small sites and high export rates coincide — 44 of the 97 measured urban sites are at or below 0.2 ha, and 90.4% of developments in urban areas send their compensation away. The residual on-site gain left behind in urban England is, in absolute terms, very small indeed.

Our own biodiversity gain plan analysis points the same way. Across all 357 plans analysed so far, 37% use off-site compensation — but that splits 42% in ONS urban authorities against 28% everywhere else. The median on-site net change tells the same story from the other end: +11.0% in urban authorities against +12.5% in non-urban ones. Urban development both delivers less at home and sends more away.

The rules have just changed — but in the same direction as before

From 6 August 2026, three changes take effect for planning applications made on or after that date. Each pushes in the same direction as the pattern set out above.

Development on sites of 0.2 hectares or less is now exempt from mandatory BNG altogether, unless on-site priority habitat is affected. Government expects this to remove around half of residential planning permissions from the regime. In our dataset it would remove 90 of the 202 sites we can measure — 45% of them — and in ONS Urban authorities, 44 of 97.

Those are precisely the sites already contributing least: 6.6% of the baseline biodiversity, and 0.021 of a unit of gain apiece. So the honest reading is that not much is being given up. But not much becomes nothing; the survey that would at least have recorded what was there is no longer required. In towns, where 45% of sites are that small, the regime stops seeing a large part of what gets built.

Minor development no longer has to try on-site compensation first. The biodiversity gain hierarchy is relaxed, so that off-site delivery counts equally with on-site provision. Our data suggests that hierarchy was doing real work: small sites currently use off-site compensation less than large ones — 34% against 42% — which is the opposite of what cost alone would predict. Remove the duty to try on-site first and that gap has only one direction in which to close.

The spatial risk multiplier is being rebased on Local Nature Recovery Strategy areas, cutting the number of habitat trading areas from 306 local planning authorities, or 159 National Character Areas, to 48 LNRS areas.

This is the change that bears most directly on the figures above, and it’s worth being exact about what it does. The BGS already distinguishes compensation that stays inside the development’s own authority from compensation that goes to a different authority in the same LNRS area. We count the second as leaving the authority, because it does, but under the new regime it will attract no spatial risk penalty at all.

Of the 2,328 developments in the current BGS register, 502 — 21.6% — will move from distant to local allocations without a single unit of habitat changing place. In Urban authorities the shift is larger still: 274 developments take the urban share compensating locally from 9.6% to 34.4%.

The reform doesn’t change where the habitat goes. It changes what the metric now treats as local with no spatial risk penalty.

What this does and doesn’t prove

  1. The two datasets count different things. The BGS covers only developments that bought off-site units. It says nothing about the majority of permissions that are met wholly on site. Our 357 gain plans are a hand-collected sample from 38 authorities, not a random one. Where the two are combined above, it’s to test an explanation, not to produce a single national rate.
  2. Hosting is inferred, not stated. The BGS register names the authority of the development but not of the gain site. We place a site in the authority whose developments record an allocation from it as ‘Within (LPA)’, which locates 145 of 212 sites carrying 81% of all units. The remaining 568 units sit on sites used by no development in their own authority; where they are is unknown, so the hosted column is the minimum measurable.
  3. Site area is not the same as the exemption area. Our site areas are based on the baseline habitat area recorded in the statutory metric, not the red line application area against which the 0.2 hectare exemption is measured. The two are close but not identical, so 45% is an estimate of how many of our sites would fall outside the new regime, not a count of them.
  4. Publication is patchy. The BGS register proves the existence of 269 gain plans across 32 authorities, but we hold no local copy of any of these. Each one is a development that cannot have begun without an authority-approved plan. Meanwhile, two authorities have now told us, in answer to FoI requests, about gain plans that are not on their own portals: one listed 60 discharge applications of which 20 could not be found, and the other scheduled six approved gain plans of which two could not be found. That’s a separate issue, but it bears on how much of this picture anyone outside a planning department can see.

Is the BNG regime delivering on its promise?

Biodiversity net gain was sold as a mechanism that would leave development areas richer in nature than it found them. What the BGS register shows, however, is that 833 area units of habitat, net, have left urban England for the countryside, with London exporting 93% of everything its developments require.

That may be defensible ecologically — larger, better-connected habitat banks can be worth more than fragmented urban parcels which may be badly delivered —  though the metric’s multipliers are meant to price that in. But it’s not what most people understood the new regime promised, and it’s happening without anyone having decided that it should. The people who lose the nature are not the people who gain it.

If the answer is that urban compensation should stay urban, the levers were there — the spatial risk multiplier, local nature recovery strategies, and the authority’s own discretion over what it accepts. Two of those three have just been loosened. The multiplier is now being based on areas seven times larger than the authorities it replaced, the duty to try on site first has gone for minor development, and a large share of urban sites will shortly sit outside the regime altogether. What is left is local discretion — and an authority that wants nature to stay in its own town will now have to ask for it explicitly, knowing the metric no longer requires it.

Note on our July 2026

Our earlier July post’s figures are not directly comparable with the figures used here. Then, we classified authorities by hand rather than by ONS category, and had only analysed 202 plans. We also reported on-site change as an average weighted by habitat value, which on a dataset with 202 records was decided by two or three large schemes — Plymouth alone moved the current figure by fourteen points. We now use the median values per plan. Our finding that urban schemes rely more on off-site compensation is unaffected.

Dataset: 357 biodiversity gain plans from 38 local planning authorities; Biodiversity Gain Sites BGS register extract of 19 August 2026 (2,328 developments, 2,686 allocations, 3,030.11 area habitat units); statutory metrics giving a measured site area for 202 plans. Authorities are classified by the ONS 2021 Rural Urban Classification of Local Authority Districts, matched by ONS area code. Bristol Tree Forum.

Our detailed analysis is available here – BGP Full Data Extract v11. However, as this is a working document which we are building on all the time, it is likely that many of the figures quoted above will have changed.

What Bristol’s biodiversity duty report doesn’t tell you

By the end of March this year, every council in England had to publish a report on what it is doing for biodiversity. Councils that are also local planning authorities — Bristol among them — must go further, and give details of the biodiversity net gain resulting, or expected to result, from the biodiversity gain plans they have approved.

This is done through the submission of a Biodiversity Gain Plan (BGP).

Some time earlier this year, Bristol City Council published its Biodiversity Duty Report (the Report) covering the period from January 2020 to December 2025. It is a handsome document, and much of it is genuinely positive: it lists 43,523 trees planted, canopy cover up to 18.2%, and pesticide use down 42%. 

On the question of BNG, though, it publishes only a single table which can’t answer the question a local resident might ask: Is new development in Bristol leaving our local nature better off or worse off?

What BNG is meant to do

Since February 2024 most new developments in England have had to deliver a 10% increase in biodiversity. Developers measure what’s on a site before they build — using a government metric calculation which converts various habitat types into ‘biodiversity units’ —  and then show how they’ll deliver at least 10% more biodiversity than was there before they started.

They can do this in three ways: improve habitat on the site itself; pay for habitat to be created somewhere else; or — as a last resort — buy statutory credits from the Government. Before building can start, the Council must approve the developer’s gain plan showing how the minimum 10% BNG will be achieved.

Each gain plan is a precise record (backed by a metric calculation) of what a development will achieve. Bristol has approved a number of these so far but the Report tells you almost nothing about what’s in them.

What Bristol actually published

Here’s everything the Council’s published about its approved gain plans, as listed in the Report:

Table from Bristol City Council's Biodiversity Duty Report summarising its seven approved biodiversity gain plans. On-site only: 3 plans, 2.56 units post-intervention, average net gain 275 per cent. Off-site only: 1 plan, 2.09 units. Combination of on-site and off-site: 3 plans, 3.56 units. Credits: none. No baseline figure is given for any row.

Look at the column headed ‘No. of Units post-intervention’. These are the biodiversity units expected after a development is completed. There’s no column for the value of the habitats that were there before (called the baseline). Without a baseline, we can’t know what the net gain percentage is. In the row labelled ‘On-site BNG only’ there’s a reported 275% average % net gain but the other rows are left blank, so it appears not to be an average across the seven plans reported. Three small schemes with very little habitat to begin with can easily produce a number like this: if a site starts with almost nothing, almost any new habitat can produce a large percentage increase. Published on its own, without the baseline values that would put it in proportion, it reads as a triumph but is meaningless because it lacks essential information.

What the gain plans we’ve examined say

Bristol Tree Forum has been collecting biodiversity gain plans from councils across England — 301 of them so far, from 34 authorities. We’ve found 18 for Bristol, 16 of which record a figure for the change in area habitat units on the development site. Twelve of the 16 lose habitat on site. Added together, the 18 Bristol plans show a net loss of 10.9 area habitat units within the red lines of the sites themselves. The four that gain contribute 0.24 units between them. One scheme, at Broomhill Road, records the loss of every unit on the site — 100%.

To be fair to the Council, most of those plans were approved during 2026 and so fall outside the period the Biodiversity Duty Report covers. However, six of them are dated on or before 31 December 2025 and belong squarely inside it; all of these six lose habitat on site, by 4.68 units between them.

Now, an on-site loss is not by itself a breach of anything. That’s exactly what the off-site habitat unit purchase option is for: where a site cannot accommodate the lost habitat on site, the developer is allowed to buy habitat units elsewhere to meet the 10% plus obligation. Nine of Bristol’s 18 plans deliver through a combination of on-site and off-site compensation, and four go entirely off-site. So, on paper, the obligation is met.

But a resident reading the Council’s report would have no idea that any of this was happening. The published table doesn’t state what the baseline habitat was or distinguish between gains and losses. It doesn’t say where the off-site habitat is. And it doesn’t name a single application, so there is no way to look one up.

Where does Bristol’s biodiversity go?

The report does contain one sentence that deserves more attention than it’s had. There’s no registered biodiversity gain site anywhere within the Bristol boundary. The Council’s own candidate sites ‘remain unregistered while a viable solution to procuring a legal agreement is worked towards’, and are still at scoping stage. As far as we’re aware, no Biodiversity Gain Site has yet been registered for the city.

That means every off-site unit bought to offset a Bristol development creates habitat outside the city. Thirteen of our 18 plans use off-site delivery in whole or in part. The habitat lost is in Bristol; the habitat created to compensate for it is not. So far, that compensation amounts to 14.60 units allocated to sites outside the city — 14.55 area units, 0.01 hedgerow units and 0.04 watercourse units. To see them, open https://bgs.bristoltrees.space/bgs-bodies, select LPA Allocation Maps and click on City of Bristol LPA on the map.

Other councils can manage it

Publishing a schedule of all the approved BGP approvals is not difficult. Other authorities are already doing it. For example, Cotswold District Council has published an appendix listing all 24 of its approved gain plans — application reference, date, delivery route, and the units and percentage change for habitats, watercourses and hedgerows on each one. Bolton publishes the same for its four, including the name of the habitat bank each one bought into. 

County Durham has not published a schedule of all its approved applications, but it has published the full Government reporting tables, which show, without flinching, that on-site habitat units across its 16 approved plans fell by an average of 30.85%.

Durham’s report is uncomfortable reading for Durham, but it is for that reason worth something; a report that cannot embarrass its author is not really a report.

What we’d like to see

Bristol has met the letter of its duty but it could have gone further and produced a meaningful schedule that would have made sense to the ordinary reader and been used to help inform a proper debate about how the city is (or is not) benefiting from the BNG regime. On our analysis, it’s not.

Three changes would fix this, and none of them requires new data — the Council already holds all of it:

  1. Publish the baseline alongside the post-development figure, so a net change can be worked out.
  2. List the approved gain plans individually, with the application reference, so anyone can find the application and check it.
  3. Say where the off-site units are, and how many have left the city.

There’s some urgency to this. The reporting cycle is five years, by which time a new Local Plan will probably have been adopted. If we have the information now, this might be used in the development of any new Local Plan so that it provides a real benefit to Bristolians. Unless Bristol chooses to publish an update voluntarily, the next time it’s legally required to tell us anything about biodiversity net gain will be 2031 — by which point seven years of development will have been permitted, built and largely finished, on the strength of a table that serves no practical purpose.

Bristol City Council’s Biodiversity Duty Report 2020–2025 is published at bristol.gov.uk. The figures attributed to gain plans in this article are drawn from Bristol Tree Forum’s own collection of biodiversity gain plans obtained from planning registers and freedom of information requests, and are ours rather than the Council’s. We’d be glad to be corrected on any of them.

The cover image above is extracted from the Council’s Biodiversity Duty Report.

Biodiversity Net Gain – what the biodiversity gain plans approved actually show

Since February 2024 biodiversity net gain has been mandatory for major development in England – and for small sites since April of that year. Two and a half years on, there’s still no publicly available national dataset of the gains that developers promised and say they’re delivering.

While the Biodiversity Gain Sites Register records off-site allocations, these are a small element of the whole BNG regime. The required biodiversity gain plans themselves — the information and documents that state, scheme by scheme, what the baseline biodiversity was and what biodiversity gain the development will deliver — sit dispersed across individual planning portals. Each portal is managed by each of over 300 planning authorities and the information is not nationally collated.

So far, we’ve collected 263 of these biodiversity gain plans from 31 Local planning authorities (about 10% of authorities). We’ve audited them field by field against the published source documents. This is what they show.

How we created the dataset

Every gain plan here was found on a local planning authority’s portal as an approved application, with a published Biodiversity Gain Plan. To date, the earliest is dated 2022; 27 are from 2024, 129 from 2025 and 91 from 2026. The authorities range from Bristol, BaNES and East Suffolk, with 18 or 19 gain plans each, down to several with just one. Site areas, where a statutory metric calculation is published and the baseline habitat area can be read from it, run from a few hundred square metres to several hectares, with a median of 0.225 ha across the 133 gain plans that we have been able to locate so far.

The sample is not representative, and depended on our being able to locate gain plans on planning portals using a variety of search approaches. These searches did not always succeed and we have probably failed to identify all the approved gain plan applications on the portals we were able to interrogate.

How we found the documents

Collecting these 263 plans was harder than analysing them. Once the right application is found, the documents are usually easy to identify: they are labelled ‘Biodiversity Gain Plan’, ‘Net Gain’, ‘metric’ or something equally simple, and the labelling is broadly consistent between planning authorities. The real challenge is finding the application on the authority’s planning portal in the first place.

A gain plan must be submitted to discharge the statutory ‘deemed’ planning condition required under the BNG regime, so it sits within a related discharge application rather than within the original permission. Finding it means knowing which discharge application to look for, and under which application type (assuming there is one). Save for the regulations, there is no guidance on how the biodiversity gain condition should be discharged or what should be published when, so every authority has settled the question differently. A minority have a dedicated application type — e.g. ‘Approval of Details – BNG’ — and one search usually returns everything, but not always : on some planning portals this search returns nothing.

For example, the Bristol City Council planning portal Advanced search option returns no decided results when the ‘Discharge Deemed BNG Condition’ Application Type is used. Only two pending applications are found, but on closer examination, even though one contains the required Biodiversity Gain Plan document, there is no required statutory metric calculation, while the other one relates to an application that predates the BNG regime.

In all other cases the only method is to guess using search terms like ‘biodiversity’, ‘BNG’, ‘gain plan’, ‘net gain’, and hope this produces results. At one authority a search for ‘biodiversity’ returned 16 results, but fewer than half were gain plan applications. At another, three search terms yielded three plans, and we still don’t know whether that’s all of them.

The problem is not that the documents are concealed; it’s that there’s no reliable way to find them, and therefore no way to distinguish an authority with few gain plans from an authority whose search term we’ve not guessed correctly. We recently submitted 41 Freedom of Information requests asking for a list of biodiversity gain plan applications, but so far only one authority has given us the information we requested (Greenwich Borough Council). The others that have replied so far, such as North Somerset Council, have refused our request on the basis that ‘The information you have requested can be found on our Planning Portal’. We have asked for an Internal Review of these refusals.

There are two further obstacles: some plans are published as scans carrying no text layer, so they cannot be searched even once located, and in four decided cases from one authority the metric is published while the gain plan is not. This is not unusual.

The practical consequence is that a member of the public who wants to know how biodiversity net gain is being delivered, say on a development near them — and even when they know the original application reference — will in many cases still not find the answer. The regime may be ‘transparent’ as a matter of law but it is unsearchable as a matter of practice.

How developers deliver the gain plan

Question 4.6 of each gain plan asks the developer how it will reach the target percentage . Across the 263 gain plans we found these answers:

4.6 answerGain Plans
On-site142
Both on and off site69
Off-site43
Both boxes ticked (contradictory)2
Unanswered7
Total263

So 112 gain plans — 43% — state that all or some part of the BNG required will be delivered away from the development site. That is a much higher rate of off-site reliance than the Biodiversity Gain Sites Register alone would suggest, because a development that delivers everything on site never appears on the register . The register can tell you where off-site provision is delivered, but not how often off-site provision is used, so it systematically understates it.

Is all the BNG required delivered?

The statutory requirement requires a minimum 10% BNG increase in area, hedgerows and watercourses habitats (it applies separately to each of these habitat modules). A scheme that adds, say, 30% of area units but fails to achieve at least a 10% increase in hedgerow units has not met the BNG requirement.

Taking area habitats, where 224 gain plans state figures we can analyse, the median net gain is +15.1%. That sounds sufficient, and for most schemes it is, but we’ve found that this value is not representative of the whole dataset. Twenty-seven gain plans record an area net gain below 10% on their own figures. Another ten record a negative area net change. The largest recorded loss is −62.7%.

There is also a long tail of very small sites recording enormous percentages: 18 gain plans exceed +100% BNG and two exceed +1,000%. These are almost all sites with a baseline close to zero — say a car park or a concrete garage base — where a handful of new planters produces a percentage gain that means very little. Any analysis that averages percentages rather than pooling units will be dominated by them.

The hedgerow and watercourse modules are where the failures concentrate. Eighty-four gain plans state hedgerow figures; the median is +72.8%, but eight fall below 10%. Only 14 gain plans state watercourse figures at all — and of those 14, five fall below 10%, one of them negative. Watercourses are rare in this sample and poorly served when they appear, so it is hard to draw conclusions from this limited dataset.

Applying the test across all modules shows that 190 gain plans meet 10% everywhere, 35 do not, and 38 cannot be assessed based what the gain plan discloses.

Where do the off-site units go, and do they exist?

One hundred and four gain plans record post-intervention units at section 7.5 of the gain plan — that is, they state an off-site position in figures. Only 73 of those can be matched to an allocation on the Biodiversity Gain Sites Register, totalling 77.88 area habitat units.

The gap between those two numbers is the most consistently troubling thing in the dataset. It has several causes, and we have separated them in the register that accompanies this piece. Some gain plans record the whole habitat bank rather than the units allocated to the development, inflating the figure by a factor of ten or more. Some repeat their section 6 on-site figures in section 7, so the same units are counted twice. Some record a positive off-site uplift with no gain site reference at 7.2 and no allocation on the register at all. Twenty-seven gain plans fall into that last category — an off-site gain asserted in an approved document, with nothing on the statutory register to correspond to it. However, it may be that these sites have yet to purchase their offsite requirements.

The reverse case also occurs: 11 gain plans have units allocated on the register while the plan itself records no off-site gain.

Unit density: more habitat, no more biodiversity

Pooling the metrics we hold — 143 metrics covering 134.5 hectares of on-site area habitat — produces a finding that percentages conceal.

 BaselinePost-development
Habitat area (ha)134.53138.25
Biodiversity units424.65424.97
Units per hectare3.1573.074

This table covers on-site area habitats only and excludes hedgerows and watercourses, which are linear habitats, and off-site purchases. It also predates the most recent additions to the dataset, so treat it as indicative of the 143 metrics we hold rather than of all 263 plans.

Across these sites, habitat area rises by 2.8% while total biodiversity units are flat, and unit density falls by 2.6%. The 10% gains recorded scheme by scheme do not aggregate into a 10% gain in on-site units, because a large share of the recorded gain is bought off site rather than created on it, and because what is created on site tends to be lower in distinctiveness and condition than what was there before. Greener, but with a lower habitat value.

What the documents show

Alongside the dataset, we maintain a register of defects — matters visible in the approved document itself, without site visits or ecological judgement. As of today it records 143 defects across 104 gain plans, from 263 held: a defect rate of 40% across 28 of the 31 authorities.

These are not close calls. They include gain plans dated before the survey they rely on; mandatory fields left blank; section 6 net-change figures that contradict the section 6.3 and 6.4 values above them; post-development values entered in the pre-development box; section 7 left empty on a gain plan that states the gain will be achieved partly off site. Every entry cites the figures it rests on, so any authority that thinks an entry is wrong can check it against its own document.

A distinct category is worth separating out. In four cases from one authority, a search of decided applications returned a statutory metric calculation but no biodiversity gain plan at all. At one of those sites the metric records the development losing 32% of the baseline area units. Off-site provision could in principle make that up — but the document that would say so, the gain plan, was not published. Under paragraph 13 of Schedule 7A, approval of the gain plan is the condition on which lawful commencement rests. It is the document that matters, and it’s the one that’s missing.

That case is worth dwelling on, because it’s the visibility problem meeting the compliance problem . A metric published without a gain plan is not a filing error. Under paragraph 13 of Schedule 7A the approved gain plan is the document on which lawful commencement depends, and it is the one document a reader cannot find. Whether it exists and was not published, or was never required, or was never produced, cannot be determined.

Why the numbers have fallen in our audit

Two months ago this analysis would have reported a defect rate of 49%. It reports 40% because we audited our own dataset before publishing it, and because we corrected it again afterwards when an authority showed us we were wrong. Both times the effect was to remove findings, not to add them.

Machine transcription fails silently. A field the extraction misses looks exactly like a field the applicant left blank, and a blank on our spreadsheet had been turning into a finding against a named authority. We compared 2,409 fields against the source documents and found 58 errors — a rate of 2.4% — of which the largest group were fields recorded as blank that were in fact fully answered.

The worst of it concerns tick boxes. Question 4.6 is a tick box, and so are 4.1, 4.7, 4.13 and 5.2. None of these PDFs stores its ticks as form data: the tick is drawn on the page, and every text extractor reports a ticked box and an empty one identically. A gain plan that answered the question looked exactly like a gain plan that ignored it. We had recorded 30 gain plans as leaving 4.6 blank and had made findings against 27 of them. Re-reading every box by measuring the ink inside it showed that all but one had answered. Thirty-one register entries were withdrawn.

We mention this because anyone building a dataset from these forms by text extraction has the same problem and may not know it. If your BNG data has tick-box fields in it, they are incorrect.

The full method, what was tested, what was found and what remains unverified, is set out in the audit statement published alongside the register. It includes the things we still cannot vouch for: only 4.6 was read in full across the whole set, and 11 of the gain plans are not on the Defra template at all, so questions cannot be said to be unanswered on them.

What this evidence fails to show

Six filters sit between this dataset and the population of approved gain plans in England:

  • The authorities are self-selecting, being those whose portals expose gain plan applications in some sort of searchable form.
  • The search of each portal may not have found every application.
  • Only decided applications are included.
  • Only published documents can be tested.
  • Fewer than half the gain plans have a metric published alongside them.
  • A blank in the dataset is not proof of a blank on the form.

The figures here should therefore be read as a floor on the rate of defects among approved biodiversity gain plans, not an estimate of it. A 40% defect rate among gain plans that were found, decided, published in full and then audited downward says nothing reassuring about the gain plans that were not found.

It is worth being explicit about what the first filter does. The authorities in this dataset are here because their portals let us find gain plans. That is not a neutral criterion. An authority that publishes its BNG documents in searchable, consistently named form is, on the face of it, an authority paying attention to the regime and the obligations it imposes. If anything, this dataset over-represents the diligent.

The dataset, the register and the audit statement are published in full below. In the meantime: we’d like to know which authorities do this well? If your portal makes gain plans easily findable, please tell us. Good practice is easier to copy than to invent.

How to fix this

Two things could make work like this unnecessary:

  • National guidance from Defra and Ministry of Housing, Communities and Local Government on how the biodiversity gain condition should be discharged and what should be published — the sort of specification the LGA’s Planning Advisory Service could write if funded.
  • A pre-submission checklist, ideally endorsed by CIEEM, covering the handful of errors that account for most of what we found.

Neither of these solutions would be difficult and both would do more for biodiversity net gain than yet another round of metric revisions. They might also, perhaps, make the life of the poor, beleaguered planning officer a lot easier!

The full dataset (263 gain plans, 31 authorities), the non-compliance register, the BGP Full Data Extract spreadsheet and the audit statement are available via the link below. The register details every defect found, with the figures it rests on.

BGP non-compliance register

Correction, 21 August 2026

An earlier version of this piece reported 159 defects across 116 gain plans, a rate of 44%. Nine plans have since been withdrawn from the register because the planning applications they discharge were made before 12 February 2024, when the biodiversity gain condition took effect: the condition did not apply to them, so no requirement of it could have been breached. Following a query from one of the authorities listed (for which, our thanks), the figures above have been amended to 143 defects across 104 gain plans, 40%. Three further entries were withdrawn on the same day after the same authority checked the off-site allocations: in two cases the units are registered and our matching had failed to find them, and in the third an apparent discrepancy is an artefact of the plan reporting to one decimal place. The dataset figures elsewhere in this piece are unaffected, as they record what the plans state rather than whether a legal requirement was met.

The cover image shows the development at Baltic Wharf which was located on the Floating Harbour in Bristol — a former caravan park that has lost 78 well-established mature trees to make way for the development.

When a city builds, where does nature go?

Since February 2024, developers in England have had a legal duty to improve the biodiversity of their development site by at least 10%. This Biodiversity Net Gain — BNG — is calculated in ‘habitat units’ using a government spreadsheet. If a scheme cannot achieve this gain on the land it’s actually building on, it can buy the shortfall from a habitat bank anywhere else in England.

The BGS register

The public register of these off-site purchases is called the Biodiversity Gain Sites (BGS) register. It lists both the authority where a development sits and the authority where the compensating habitat is purchased.

We looked at all 2,441 allocations on the register, covering 301 local planning authorities. We found that, across the board, 79% of the allocations send the compensation to a local authority far from the development itself. That is striking enough. But the pattern sharpens dramatically in the more urban areas.

For example, in London, 98% of allocations are delivered outside the borough where the building happens. Just 3% stays within it. London’s boroughs have generated external demand for 46 habitat units and host barely three in return. Metropolitan districts — such as Manchester, Sheffield, Leeds and Birmingham — send 88% of their compensation elsewhere.

By contrast, non-urban authorities send 74%, and keep habitat within their own boundaries in 42% of cases, against London’s 3%.

Taken together, urban authorities are net exporters of habitat. The countryside is where it lands – often in remote rural locations few will ever visit.

How far away does nature go?

The register also records the distance between each development and the habitat bought to compensate for it. The typical distance is 37 km — roughly 23 miles. One allocation in five is more than 100 km away from its development site.

Median distance from development to compensating habitat, by type of authority

For London the median is 86 km, and nearly half of the capital’s allocations are more than 100 km away. Two-thirds fall into the register’s most distant category — the same category the rules are meant to discourage.

Who loses out?

Each site can be placed on a national deprivation scale, from decile 1 (the most deprived tenth of neighbourhoods) to decile 10 (the least deprived). Comparing where a development happens with where its habitat ends up gives a rather uncomfortable picture.

Average deprivation decile of the development, and of the habitat created to compensate for it

Development in metropolitan districts sits, on average, in decile 4.0 — among the more deprived parts of England. The habitat created to compensate for it sits in decile 6.3. Nationally, the shift is from 6.0 to 6.6, and it is almost entirely driven by cities.

Of the 504 allocations where the development is in one of the three most deprived deciles, 99% send their habitat somewhere less deprived — landing, on average, in decile 6.5. For non-urban authorities there is essentially no movement at all.

Displacement, not disappearance — but that is not the whole story

It is worth being careful here. Habitat units are being created. This is displacement, not straightforward destruction, and the register shows real habitat banks being funded and monitored.

Nor is this purely an urban phenomenon. The largest single net exporters on the register are Cherwell in Oxfordshire and Westmorland and Furness — not cities, but high-growth areas under development pressure. Land scarcity, not city status, is the underlying driver.

But displacement still matters, for reasons the metric does not capture. A hectare of habitat in a dense neighbourhood serves thousands of people who can visit it, but the same hectare 50 miles away, on a farm almost nobody visits, scores identically in the register. Access, shade, cooling, birdsong on the way to school — none of these elements appear in the data.

The rules do include a brake: compensation delivered further away is discounted, by a quarter if it’s in a neighbouring area and by half if it’s farther still. On this evidence, though, the brake is not holding, and the latest plans propose to remove it altogether for many developments, making it still worth buying habitat miles away.

What the gain plans show

We also read 205 individual gain plans in detail. The contrast is just as clear on the ground.

Developments in urban authorities lost area habitat on site — down 8% overall between the ‘before’ and ‘after’ figures in their own calculations — while developments in rural authorities gained 16%. Yet both groups have to demonstrate the same 10% or more net gain. Urban schemes get there by buying it: 54% of them use off-site compensation, against 33% elsewhere. Often this is simply because there are just no local Biodiversity Gain Sites, so the developer has no local options.

This is not a story about small development sites. The average development we measured was almost exactly the same size in urban and rural authorities — around 0.7 hectares. It is about the scarcity of available urban land, which is reflected in its cost, not the size of the plots.

The question worth asking

BNG is a real advance on what came before, and the register is a genuine piece of public transparency. This analysis is only possible because the data is published.

But if the policy’s promise is that development leaves nature better off, it is fair to ask: better off for whom? On current evidence, the answer in our biggest cities is someone else, somewhere else — on average 37 kilometres away, in a less deprived place.

Here is our detailed analysis:

Where does the biodiversity go?

Analysis by Bristol Tree Forum, using the Biodiversity Gain Sites register (2,441 allocations to 28 July 2026) and 205 biodiversity gain plans transcribed from local planning authority records. Charts and underlying data at bgs.bristoltrees.space.

Ancient trees, missing data, and the fight over Bristol Airport’s planned expansion

So far, most of the public alarm about this expansion has centred on Felton Common, the well-loved local nature reserve on the other side of the runway, where the airport wants to plant 8.5-metre approach lights and fencing across protected grassland. Campaigners under the Save Felton Common banner have campaigned hard against that ‘land grab’, and rightly so. But the fierce fight over the Common has largely overshadowed a second, quieter yet important threat next door — the loss of irreplaceable habitat at Cook’s Farm, which has drawn far less attention. That is what our objection is chiefly concerned with.

Bristol Airport wants to grow. Its planning application (ref. 26/P/0686/OU2) seeks permission to expand from 12 million passengers a year to 15 million. To do this, the airport needs more land — including Cook’s Farm, some 24 hectares of long-established agricultural countryside where hedgerows have stood since at least the 1840s and where some trees have been growing for centuries. The airport now proposes to compulsorily purchase the site so it can carry out its plans.

However, it first needs to persuade the planners that its proposal is acceptable. We say it’s not, and we’ve lodged a detailed objection. It is a technical document, full of hectares and habitat codes, but underneath the detail is a simple story: irreplaceable habitat is at risk, the evidence supporting the plans doesn’t add up, and the law says that should matter.

Here is what our objection says, in plain terms.

The heart of it: three veteran trees

The most emotive part of the case concerns three veteran trees growing in an ancient hedgerow on the boundary of Cook’s Farm — two Ash and one Sycamore. The airport doesn’t propose to simply cut them down. Instead, it plans to translocate them: lift them with a giant tree spade and replant them on the northern edge of the development.

That might sound like a reasonable compromise, but our objections explain why it’s not in careful detail.

A veteran tree isn’t just an old tree, especially those in long-established hedgerows. It’s a whole ecosystem — cavities, rot, deadwood and fungal growth that specialist insects, fungi and other wildlife depend on and cannot find anywhere else. These features take centuries to form. You cannot manufacture them, and you cannot move them.

Worse, veteran trees are extremely unlikely to survive being moved. Their biology works against them. Over centuries they’ve spent their reserves coping with drought, storms, disease and damage, leaving little in the tank to survive the shock of relocation. Their roots are extensive but fragile, they depend on specialised underground fungal networks built up over generations, and much of their internal wood is effectively dead but structurally essential — it can’t be repaired if damaged. Successful relocation needs around two full growing seasons of careful root preparation beforehand. Crucially, the airport’s plan makes no proposal to reduce the trees’ roots at all. As our objection bluntly puts it: if the trees are translocated without root reduction, they will die.

Our conclusion is that, for the purposes of a planning decision, these three veteran trees should be treated as lost. The airport itself seems to half-accept this: it promises a ‘compensation’ package of ten new future veteran trees and the artificial ‘veteranisation’ of ten existing trees. But you can’t conjure a veteran tree on demand. Even with the right conditions, it takes two or three decades for a ‘veteranised’ tree to start resembling the real thing — and it will still lack the fungal decay that gives a true veteran its ecological value.

The evidence doesn’t add up

Beyond the trees themselves, we found that the environmental evidence supporting the application is riddled with inconsistencies. This means that the application can’t properly be decided as it stands.

The airport is required to demonstrate that it will deliver ‘Biodiversity Net Gain’ — a calculation meant to prove development leaves nature in a measurably better state (at least 10%) than it was before development. But our objection shows the numbers in the official metric calculation simply don’t match the airport’s own ecological survey. The two documents use different habitat categories, different reference codes, and don’t cross-reference each other. Some habitats that appear in the survey are missing from the metric altogether. Habitat parcels aren’t sized, and their locations aren’t shown on the map. In short, it’s impossible to reconcile the airport’s own datasets.

The tree surveys are a particular problem. Three surveys tucked into the appendices fail to meet BS5837:2012, the British Standard for trees in planning. Between them they’re missing the surveyors’ names and qualifications, survey dates, crown-spread data, branch heights and directions, life-expectancy estimates, soil assessments, and even the number of trees in some groups. One key survey dates from June 2024 and is now out of date. And when we asked for the tree schedule in a usable spreadsheet format so we could check it, our request was refused — leaving them, in their words, to analyse the data ‘as best we can’.

Even working with that inadequate evidence, their interim analysis is striking. Of roughly 1,618 individual trees on the site, some 367 — more than a fifth — are set to be removed, along with a share of the site’s hedgerows, which the airport’s own figures and the survey record in wildly different numbers (10 hedgerow parcels in one document, 71 in another).

Why this is a matter of law, not just sentiment

This is where our objection turns from ecology to policy — and it’s the part that could decide the outcome.

National planning rules are clear about irreplaceable habitats. Paragraph 193(c) of the National Planning Policy Framework says development that causes the loss or deterioration of irreplaceable habitats — and it names ancient and veteran trees specifically — ‘should be refused, unless there are wholly exceptional reasons and a suitable compensation strategy exists’.

We make two arguments about this test:

  • First, it’s a two-part test that has to be met in sequence: you need both wholly exceptional reasons and a suitable compensation strategy. A compensation package — however good, and here they say it isn’t good — cannot on its own make the reasons ‘wholly exceptional’. The decision in Juden v London Borough of Tower Hamlets [2021] EWHC 1368 (Admin) backs this interpretation.
  • Second, we argue that this scheme doesn’t clear the ‘wholly exceptional’ bar at all. The Framework’s own example of exceptional reasons is nationally significant infrastructure — the kind of once-in-a-generation project decided by government. This application, we say, is simply about increasing the capacity of an existing airport. That’s not the sort of wholly exceptional circumstance the rules have in mind.

Our objection also points to local policy. North Somerset Council’s own adopted Core Strategy (Policy CS4) requires it to protect, connect and enhance important habitats, ‘particularly designated sites, ancient woodlands and veteran trees’. The same protection is included in the Council’s emerging 2041 Local Plan. Approving the loss of these veteran trees would go against the Council’s own rules.

What it comes down to

Strip away the appendices and the acronyms, and our case is straightforward. The airport wants to expand on to land that includes centuries-old, irreplaceable habitat. Its plan to ‘move’ three veteran trees is, on the evidence, a plan to kill them slowly. The paperwork meant to justify all this is inconsistent, incomplete and in places non-compliant with the relevant standards. National and local planning policy both say irreplaceable habitat like this should be protected, not traded away for extra passenger numbers.

Our central demand is modest but firm: these problems need to be resolved before the application can properly be decided. For anyone who cares about Cook’s Farm, its ancient hedgerows and the veteran trees growing in them, that’s the line worth holding.

Here is our full response to the application:

BTF Consolidated Comments – 06 May 2026

Understanding Biodiversity Gain Plans

Since BNG became mandatory in February 2024, qualifying developments in England must show how they will deliver at least a 10% gain, to be set out in a Biodiversity Gain Plan (BGP) submitted to the local planning authority. We’ve transcribed 160 BGPs from 21 LPAs into a single, comparable dataset.

What the data shows so far:

  • Just over under 60% (95 of 160) deliver their gain entirely on site. Another 34 use a mix of on-site and off-site measures, while 17 rely wholly on off-site units and 14 did not state an approach. Two bought Statutory Credits.
  • Off-site reliance is a recurring theme. A number of plans record an on-site biodiversity loss offset by purchased habitat units — a legitimate route, but one that moves the gain away from the community where the development happens.
  • Net gain has to be met habitat type by habitat type (area, hedgerow, watercourse), not as a single blended figure. Several plans that pass overall are marginal — or fall short — on an individual module.

Accessing this data was harder than it should be:

  • There is no central register of gain plans – why can’t Defra or Natural England include them in their BGS allocation dataset? These documents should be easily accessible.
  • Each council’s portal has to be searched separately, with no consistent way of identifying the relevant application. Only a few authorities (City of York, Bristol and Cotswold among them) have a dedicated application category for BNG discharges. Otherwise the BGPs sit inside generic “discharge of conditions” applications and are very difficult to find.
  • BGPs are produced in a variety of forms – as clean PDFs, fillable forms, bespoke versions or scanned images requiring OCR – which is challenging, especially if they are hand-written.
  • They are often internally inconsistent: off-site figures just copied from the on-site section, credits confused with habitat-bank units, or headline numbers that do not reconcile.
  • Off-site claims frequently differ from what the Biodiversity Gain Sites register records as allocated.
  • Many applications do not include the required BNG Metric calculation.
  • Some applications can’t be analysed because all that is produced (and approved) is the certificate of the off-site HU purchase – and sometimes not even that. As a result, we’ve been unable to include these in our analysis.

The information exists, but we can only conclude that the planning approval process makes meaningful public scrutiny far harder than it needs to be. Using the available standard Defra form and creating a single searchable register of BGPs would be a straightforward improvement.

The full dataset and analysis are here — comments, corrections and more data are welcome:

BGP Full Data Extract

NB. This analysis will grow as we add more data.

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