You seemed to be using Biodiversity Net Gain (BNG) as the proxy for harm, so that the reported net gain of nearly 3% was sufficient to conclude that there was no ‘harmful impact’ as defined by DM19.
Bristol Local Planning Policy DM19 plainly states that ‘Development which would have a harmful impact on the nature conservation value of a Site of Nature Conservation Interest will not be permitted.’ It could not be clearer.
If your interpretation of this is correct (and we say it cannot be), it will effectively nullify any policy protection for SNCIs or indeed, any other existing green infrastructure and all SNCIs could be developed in a free-for-all. We set out our reasoning below.
The Mitigation Hierarchy
The Mitigation Hierarchy, as enshrined at paragraph 180 a) of the NPPF, states:
When determining planning applications, local planning authorities should apply the following principles:
a) if significant harm to biodiversity resulting from a development cannot be avoided (through locating on an alternative site with less harmful impacts), adequately mitigated, or, as a last resort, compensated for, then planning permission should be refused;
On your interpretation, the first element of this cascading test, avoidance, will never have to be applied. Instead, you need only consider the second element, mitigation, for it is only then that ‘harm’ can be assessed. This cannot be the intention of this provision.
Green spaces protection
The effect of your approach is to make a nonsense of the prohibition against causing any ‘harmful impact’ to an SNCI as conferred by DM19. It effectively nullifies the special protection given to these sites. Here is the full DM19 policy wording:

On your interpretation, the whole section relating to Sites of Nature Conservation Interest may as well be deleted, as it adds nothing to the more general policy set out above.
The section relating to wildlife corridors is also rendered meaningless if there can now be no net ‘harmful impact’.
The same conclusion must also apply to the protection of Urban Landscapes under SADMP DM17, another feature which ‘contributes to nature conservation in Bristol’, on your interpretation. Your interpretation might also be extended to the other Existing Green Infrastructure identified in DM17.
Achieving BNG means there is no ‘harm’
When the Environment Act 2021’s requirement for all developments to achieve at least 10% biodiversity net gain takes effect later this year, it must follow that schemes which achieve this will have caused no ‘harm’ under your definition.
How then should this be interpreted if the net gain can only be achieved through offsite mitigation (as will often be the case)? Even in this scenario, it seems that there can never be any circumstance where an SNCI can suffer a harmful impact because it must always be mitigated by the requirement to achieve at least 10% BNG. It is even possible to imagine that the SNCI status of the target site will be lost as a result of the development, yet, as you see it, this will not be ‘harm’.
You are in effect stating that no SNCI in Bristol now has any greater protection than any ‘other habitat, species or features, which contribute to nature conservation in Bristol’ and the whole special status of SNCIs has become meaningless.
This cannot be what was intended when SNCIs were created and given special protection under the Local Plan.
We urge you to reconsider your advice.
Our statement to the Planning Committee can be read here.
A copy of this letter may be downloaded here