Biodiversity Net Gain in Local Plans and Strategic Planning

Webpage updated 11 July 2023 The Environment Act 2021 makes a 10% biodiversity net gain mandatory from January 2024. By this date Councils will need to be able to assess and determine planning applications and their associated biodiversity gain plans to check that they are legally compliant. Once the mandatory requirement for BNG is in place, there is no technical need to repeat the legal requirements in local policy. However, BNG is already required through national planning policy in England and Wales and experience has shown that a clear Local Plan policy helps to ensure this is delivered locally.

You can find more information about current national planning policy on our Biodiversity net gain now and in the future page.

We would encourage LPAs to develop a locally specific BNG policy in their local plan for the following reasons:

  • Where the local plan policy is in place before BNG becomes mandatory, it allows the authority to explore and test applications of BNG prior to the legislative requirements. It will also prevent a situation where applicants rush to submit planning applications before the requirement is mandatory in order to avoid including BNG.
  • A locally-specific policy allows a local authority to set out any local priorities and strategies they require developers to take into account in delivering BNG, e.g. locally important habitats, Biodiversity Action Plans, Green Infrastructure strategies and Local Nature Recovery Strategies (LNRS). This will help to target offsite BNG delivery and determine the ‘strategic significance’ score that is part of the Biodiversity Metric.
  • As such, a locally-specific policy can help to ensure that BNG contributes to wider nature recovery plans in addition to local objectives. It can help ensure that the right habitats are provided in the right places.
  • Including BNG policies in the Local Plan can link biodiversity to other strategic objectives and the overall place-making strategy for an authority, enabling a more holistic approach. For example, this could be recreation and health, flood risk alleviation, active travel or the more comprehensive climate emergency ambitions of a council.   

In our view, developing a policy approach to biodiversity net gain prior to the mandatory requirement coming into force needs to consider:

  • Evidence to inform the local policy, including evidence to demonstrate that the approach taken will be viable
  • Setting out local priorities for biodiversity net gain, including whether on-site BNG is preferred and how and where off-site BNG should be delivered
  • Setting a target for BNG delivery
  • Setting a metric for measuring BNG
  • Setting requirements for management and maintenance of habitats provided

Section 3.12 of Dartmoor National Park's Local Plan Topic Paper on the Natural Environment (see also below under Evidence) provides an excellent summary of the challenges of developing policy prior to BNG becoming mandatory, as well as justification for the BNG policy they have included in their (now adopted) Local Plan.

You might also want to develop a Supplementary Planning Document to set out details of the approach and set a strategy for off-site delivery.

Listed below are some good examples of locally-specific policies on BNG in current 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. We also 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.

Feedback welcomed on this page and please do share your examples with us: [email protected].

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.

Martin from PAS presented on BNG in Local Plans, and Fiona Fryer from Salford City Council and Dan Knowles from Guildford Borough Council shared their experience on BNG in their adopted Local Plans at Natural England's Norfolk and Suffolk BNG Planning Partnership Group meeting on 28 June 2023. A recording of Martin and Fiona's presentations is available on YouTube and Martin, Fiona and Dan's slides are also shared as PDFs and via Slideshare at the bottom of this page.

Local plan policy examples

Supplementary Planning Documents

Other policy guidance documents

Evidence for Local Plans

In the interim period before biodiversity net gain is mandated through the Environment Act, you will need some evidence to support your Local Plan policy if you set a percentage target, as the National Planning Policy Framework (NPPF) and Natural Environment Planning Policy Guidance (PPG) do not include a target or reference to the Biodiversity Metric: see our Biodiversity Net Gain now and in the future page for further information on current national policy.

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 ( 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: The 14 authorities whose local plans would require developers to deliver a biodiversity net gain of over ten per cent and Carter Jonas study on Biodiversity Net Gain in local plans.

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: 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.

Presentations on Local Plans from Natural England's Norfolk and Suffolk BNG Planning Partnership Group meeting on 28 June 2023

Martin from PAS presented on BNG in Local Plans, and Fiona Fryer from Salford City Council and Dan Knowles from Guildford Borough Council shared their experience on BNG in their adopted Local Plans at Natural England's Norfolk and Suffolk BNG Planning Partnership Group meeting on 28 June 2023. Their presentations are shared here as PDFs. If you would like an accessible version of these documents, please email [email protected].