Webpage updated 22 May 2025, but note that example Local Plan policies and evidence were compiled in 2023 and are not up-to-date good practice. The Environment Act 2021 makes a 10% biodiversity net gain mandatory for Town & Country Planning Act development with a few exceptions. This legislative requirement does not need to be duplicated in policy, but there are good reasons to include policies in Local Plans that complement the statutory framework to support BNG implementation.
You can find an introduction to BNG on our Biodiversity Net Gain for local authorities webpage. Further information on Local Plans and BNG is available in the BNG PPG Paragraph: 006 Reference ID: 74-006-20240214. Paragraph: 020 Reference ID: 74-020-20240214 covers how existing local policies apply following the introduction of mandatory biodiversity net gain.
LPAs do not need to repeat the mandatory requirement for BNG in policy. They should also make sure that they do not include policies or guidance which are incompatible with this framework. However, we would encourage LPAs to develop locally specific policies in their local plan to complement the BNG framework, as long as they are consistent with the legal framework. The local authority should also consider setting out how they baseline, measure and monitor BNG delivery as part of Local Plan monitoring.
Some local authorities are considering setting a policy for a BNG target above 10%. This will need to be backed up by appropriate evidence, including that the approach taken will be viable – see below for further information. Note that Policy N1: Identifying environmental opportunities and safeguards of the consultation draft National Planning Policy Framework (NPPF) states that Local Plans will only be able to set local standards for biodiversity net gain which are in excess of the statutory net gain requirement for specific site allocations. The National Planning Policy Framework consultation document states on P.106: Transitional Arrangements: ‘we are proposing that development plan policies should be afforded very little weight where inconsistency arises,’ meaning that existing LP policies that go above the statutory requirements should be afforded very little weight unless for specific site allocations, if this comes in.
For general advice on integrating BNG into your Local Plan, Section 4.2 of the CIEEM/IEMA/CIRIA Biodiversity net gain good practice principles for development covers evidence gathering and provides further detail on types of evidence and links to good practice, whilst Sections 4.6 and 4.7 cover policy development.
We have a practitioner network for local authority officers interested in BNG, which acts as a group to discuss and share best practice on BNG. If you wish to join this network, please fill out this Microsoft Form.
****THE CONTENT BELOW WAS COMPILED IN 2023 PRIOR TO THE IMPLEMENTATION OF BNG AS A STATUTORY REQUIREMENT AND WILL NOT NECESSARILY COMPILE WITH CURRENT GUIDANCE OR THE STATUTORY BNG REGIME.****
WE WILL BE UPDATING THIS PAGE WHEN PLANNING POLICY FOR BNG IS UPDATED IN 2026.
Listed below are some good examples of locally-specific policies on BNG in local plans, Supplementary Planning Documents and other planning policy guidance documents, as well as some links to evidence for developing BNG policy in Local Plans.
Feedback welcomed on this page and please do share your examples with us: [email protected].
Local plan policy examples
Supplementary Planning Documents
Other policy guidance documents
****THE CONTENT BELOW WAS COMPILED IN 2023 PRIOR TO THE IMPLEMENTATION OF BNG AS A STATUTORY REQUIREMENT AND WILL NOT NECESSARILY COMPILE WITH CURRENT GUIDANCE OR THE STATUTORY BNG REGIME.****
WE WILL BE UPDATING THIS PAGE WHEN PLANNING POLICY FOR BNG IS UPDATED IN 2026.
Evidence for Local Plans
In the interim period before biodiversity net gain was mandated through the Environment Act, LPAs needed to provide evidence to support their Local Plan policy if it set a percentage target, as the National Planning Policy Framework (NPPF) and Natural Environment Planning Policy Guidance (PPG) did not include a target or reference to the Biodiversity Metric.
Some examples of evidence used to support BNG policy in adopted Local Plans are provided below. There is also further information about viability assessment to inform percentage targets for BNG below.
We are aware of a couple of examples where BNG policies requiring a particular percentage target have been challenged, hence the need for robust evidence to support policies:
- Rossendale Borough Council has dropped any BNG percentage in the final version of its plan, despite proposing the adoption of a 20 per cent minimum BNG requirement in its draft local plan. The adopted version of Rossendale’s plan states that the authority will "seek biodiversity net gain consistent with the current national policy”. In her report, Inspector Katie Child stated that the council had provided “insufficient justification for either a 10 per cent or 20 per cent net gain in either green infrastructure or biodiversity, when only net gains are currently required by the Natural Environment PPG”.
- Fareham Local Plan have had some challenges to their BNG policy. Paragraph 53 of the Inspector's initial findings letter: Post hearings letter (fareham.gov.uk) summarises the Inspector's initial views on the policy.
Examples of evidence to support Local Plan BNG policy
Local Plans, viability and percentage of net gain
Warwickshire County Council undertook a feasibility assessment of introducing biodiversity accounting in Buckinghamshire and Milton Keynes in 2019. The study covered viability, but the conclusion was that viability impacts can only be assessed on a case-by-case basis and then factored in at the concept/design stage for an individual proposal. A developer can then consider BNG in combination with other contributions and factor it in to land purchase.
Salford Borough Council assessed the impacts of BNG on viability for their Local Plan and a background paper sets out the conclusions of this, alongside other issues raised with their Local Plan policy for 10% BNG. The conclusion was that 'net gain delivery costs are low as a proportion of overall costs'.
In terms of the percentage of net gain, a sensitivity analysis was carried out as part of the Defra impact assessment to look at impacts of 5% BNG, 10% BNG and 20% BNG, the conclusion being:
While this suggests that varying the level of net gain between 5% and 20% has very limited impact on the outcome, there is a trade-off between cost implications for developers and the likelihood of net gain being delivered at a national level (e.g. less costly/likely at 5% net gain compared to 10%, and vice versa for 20%). Our chosen policy approach, which sets out that 10% is the right level to demonstrate net gain, considers this trade-off among other issues.
Going above 10% BNG
Some local authorities are looking to go above 10% as a target. Further information is provided in this Planning Resource article Seven councils have published local plans requiring a biodiversity net gain of more than 10%, report reveals and Carter Jonas study on Biodiversity Net Gain in local plans. Evidence for such policies is covered in Paragraph: 005 Reference ID: 74-005-2023 of the draft BNG PPG.
Guildford Borough Local Plan: Development Management Policies (part 2 of the Local Plan) was adopted on 22 March 2023 with Policy P7: Biodiversity in New Developments requiring 20% BNG once BNG becomes mandatory. The main evidence to support 20% net gain in this case was Surrey Nature Partnership's recommendation for 20% BNG and the policy was also tested through the Viability Assessment, which you can find on Guildford Borough Council's Submitted documents webpage. Further evidence was submitted to support the policy under Matter 3 during the Examination, including a specific study. See Dan Knowles from Guildford Borough Council's presentation from June 2023 on their approach below.
The Kent Nature Partnership net gain group has published a county-wide strategic viability assessment to understand the implications of a 20% BNG approach for Kent: https://kentnature.org.uk/nature-recovery/biodiversity-net-gain/. In summary:
- A shift from 10% to 15% or 20% BNG will not materially affect viability in the majority of instances when delivered on-site or off-site.
- The biggest cost in most cases is to get to mandatory, minimum 10% BNG. The increase to 15% or 20% BNG in most cases costs much less and is generally negligible.
- Because the BNG costs are low when compared to other policy costs, in no cases are they likely to be what renders development unviable.
- Local Authorities who wish to pursue BNG in excess of 10% will need a local viability assessment to support it. However, this study shows an assessment is likely to demonstrate viability will not be negatively impacted (to a material extent) for BNG increases of up to 20%. Because costs are small BNG is unlikely to impact the viability threshold significantly.
- If onsite provision is how the majority of BNG is delivered, this could have implications on land take as a result of lowering of average housing densities. However, as the majority of this burden relates to the mandatory 10% BNG, and the increase to get to 15% and 20% BNG are comparably small, this should not be seen as a reason for not going beyond the 10% but is a consideration for LPAs.
Swale Borough Council used the Defra impact assessment ‘central estimate cost per dwelling for the South East’ for their draft Local Plan Viability Study. This looked at the difference between provision of 10% and 20% BNG and put costs at £948 per dwelling for 10% BNG with an additional £180 per dwelling for 20% BNG. Swale BC recently consulted on their pre-submission Local Plan Review which included a policy for 20% net gain.
DISCLAIMER: The PAS team updates these pages regularly to reflect current guidance on biodiversity net gain as best we can. Our goal is to provide accurate, timely information to support local planning authorities. If you are from a local authority and have any questions about the content or need further information, please contact us at [email protected]. This page was last updated on 02/10/25.