Biodiversity Net Gain in Local Plans and Strategic Planning

The Environment Act 2021 makes a 10% biodiversity net gain mandatory from an as-yet unconfirmed date expected to be in November 2023. 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 will be adding to these as part of this PAS project. We will also share ways that you can start implementing BNG if your current Local Plan does not cover net gain. Feedback welcomed on this page and please do share your examples with Beccy Moberly.

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.

Local plan policy examples

Plymouth and South West Devon Local Plan 2019

Policy DEV 26 Protecting and enhancing biodiversity and geological conservation (Page 286) sets out that net gains will be required from all development and that these should be designed to support the local biodiversity network. More detail on the application of the biodiversity net gain approach is set out in the accompanying Supplementary Planning Document - see below.

Dartmoor Local Plan 2021

Strategic Policy 2.3 Biodiversity Net Gain (Page 40) requires that development involving 2 homes, 100m2 of non-residential floorspace or a site area of 0.2 Hectares, or more delivers 10% biodiversity net gain. 'Off-site enhancement will only be acceptable where on-site provision is not possible, or it would make a better contribution to improving biodiversity than wholly on-site provision.' The policy also refers to enhancing the National Park’s network of wildlife sites and priority habitats and maximising potential for other environmental gains.

Arun Local Plan 2018

Policy ENVDM5 Development and Biodiversity (Page 218) sets out that development schemes shall seek to achieve a net gain in biodiversity and protect existing habitats as well as creating links to facilitate a network of greenspaces. Policy ENV DM3 Biodiversity Opportunity Areas states that development proposals that do not reasonably address opportunities for enhancing locally valued and important habitats will be refused.

Leeds Local Plan Core Strategy 2014 (Amended 2019)

Policy G9 Biodiversity Improvements (Page 122) requires that development achieves an overall net gain for biodiversity commensurate with the scale of the development, including a positive contribution to the habitat network through habitat protection, creation and enhancement. Further information for developers is set out in Leeds' biodiversity guidance for developers - see the Development Management examples for details.

South Oxfordshire Local Plan 2020

Policy ENV 3: Biodiversity (Page 168) 'All development should provide a net gain in biodiversity where possible. As a minimum, there should be no net loss of biodiversity. All proposals should be supported by evidence to demonstrate a biodiversity net gain using a recognised biodiversity accounting metric.' The Policy is supported by Guidance to Developers and Ecological Consultants - see the the Development Management examples for details.

Tewkesbury Borough Plan 2022

Policy NAT1 Biodiversity, Geodiversity and Important Natural Features (P.109) 'Proposals will, where applicable, be required to deliver a biodiversity net gain across local and landscape scales, including designing wildlife into development proposals, the connection of sites and large-scale habitat restoration, enhancement and habitat re-creation. Locally defined ecological networks identified in the Local Nature Recovery Strategy will be the primary focus for landscape scale net gain delivery.' Supporting text states that before BNG becomes mandatory the Council expects all major developments to deliver a minimum net gain of 10% calculated using the Defra Biodiversity Metric and that BNG should be delivered on-site preferentially.

Publication Salford Local Plan: Development Management Policies and Designations 2020

Policy BG2 Development and biodiversity (Page 219) requires all development to deliver a net gain in biodiversity value and all major development to deliver at least a 10% net gain in biodiversity value. It also sets out a hierarchy for compensation with on-site preferred and then off-site in the local area, plus the need for management, monitoring and reporting for 25 years. A modification to the publication policy adds a paragraph to set the baseline as before any site clearance or other activities that have lowered the biodiversity value of the on-site habitat after 30 January 2020 other than in accordance with planning permission: PM001 - Schedule of proposed main modification (salford.gov.uk). Refers to GMCA Biodiversity Net Gain Guidance for Greater Manchester - see below

Note that the Inspector's Report on the examination Salford Local Plan is now available. The only amendment to Policy BG2 is to clarify and ensure that pre-development biodiversity value is assessed at an early stage and recorded prior to any new development activity on site to make it effective.

Bassetlaw Local Plan Publication Version 2022

Policy ST40 Biodiversity and geodiversity (Page 142): 'All new development should make provision for at least 10% net biodiversity gain on site, or where it can be demonstrated that for design reasons this is not practicable, off site through an equivalent financial contribution.' Supporting paragraphs refer to the need for BNG to be on-site: 'Only in exceptional cases where this is not practicable will compensatory off site contributions be appropriate'. The policy also refers to the need for development to establish additional ecological links to the Nature Recovery Network.

Note that financial contributions for off-site compensation are not likely to be consistent with the mandatory system for biodiversity net gain, as this will require appropriate off-site BNG to be secured prior to commencement of development.

Barnet Draft Local Plan (Reg 19 submission) 2021

Policy ECC06 Page 239 requires that development makes the fullest contributions to enhancing biodiversity and protects existing site ecology, plus that at least the required level of biodiversity net gain, stated by regulation, is attained.

Supplementary Planning Documents

Plymouth and South West Devon Supplementary Planning Document 2020

Policy DEV 26.5 Biodiversity Net Gain (Page 128) requires a 10 per cent increase in biodiversity units when applying the Defra Biodiversity Metric. It sets out how BNG should be applied for major and minor development and the requirement for a Biodiversity Budget. It sets out various alternatives for off-site delivery when sufficient on-site BNG can not be achieved or there is a clear benefit. It directs applicants to support delivery of the local Biodiversity Network, as identified in the Local Plan.

Buckinghamshire Biodiversity Net Gain Supplementary Planning Document 2022 

Buckinghamshire Biodiversity Net Gain SPD includes a flowchart for the net gain process and detailed guidance on what is required and how applications will be determined by Buckinghamshire Council, securing BNG on- and off-site, as well as monitoring and reporting requirements.

Lake District National Park Biodiversity Supplementary Planning Document 2021

Lake District National Park Biodiversity SPD sets out how the council will achieve BNG through planning applications, including: the biodiversity information required when submitting a planning application; how to apply the mitigation hierarchy; and how offsite compensation will be secured. It includes a need to use Defra's Biodiversity Metric, ensure a 10% gain and submit a Biodiversity Gain Plan. There is an option to provide a financial contribution for off-site net gain, where the BNG requirement can not be met on-site.

Biodiversity Supplementary Planning Document For Northamptonshire 2015

Biodiversity SPD For Northamptonshire is focused on biodiversity more broadly - not just habitat enhancement, i.e. BNG. It sets out a step-wise process for building nature into development, including aftercare, and includes a biodiversity checklist as an appendix.

Harrogate Providing Net Gain for Biodiversity Supplementary Planning Document (SPD) 2021

Harrogate Providing Net Gain for Biodiversity SPD sets out how to assess a site, how to design a scheme and when to use offsetting, with a requirement for applicants to submit a Biodiversity Enhancement Management Plan. It also includes a Strategic Significance Map to inform the strategic significance score in the Biodiversity Metric.

Greater Cambridge Shared Planning Biodiversity Supplementary Planning Document 2022

Greater Cambridge Shared Planning Biodiversity SPD covers biodiversity in planning as a whole, including designated sites and protected species, as well as BNG. It sets out the legal and policy context, including local biodiversity strategies, highlights the existing local biodiversity resource and then sets out a stage-by-stage process to considering biodiversity and achieving biodiversity net gain through the development management process.

Cheshire East Draft Biodiversity Net Gain SPD, 2021

Cheshire East Draft Biodiversity Net Gain SPD sets out the policy context and draft principles for applicants on achieving BNG in terms of what they should do and how they should do this with a requirement for a Biodiversity Net Gain Report and use of the Defra Biodiversity Metric. There is a requirement for applicants to demonstrate how they are contributing to the local Ecological Network (as set out in Local Plan policy) and to set out plans for management and monitoring. It also includes guidance on commuted sums, where the applicant is unable to secure net gain on-site or themselves off-site.

Other policy guidance documents

GMCA Biodiversity Net Gain Guidance for Greater Manchester 2021

GMCA Biodiversity Net Gain - Guidance for Greater Manchester

Cornwall Council Climate Emergency DPD

Cornwall Council Climate Emergency DPD

New Forest District Council Ecology and BNG Interim Advice Note

New Forest DC Ecology and BNG Interim Advice Note

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 (fareham.gov.uk) summarises the Inspector's initial views on the policy.

Examples of evidence to support Local Plan BNG policy

Plymouth and South West Devon Biodiversity Network Creation process 2017

Plymouth and South West Devon Biodiversity Network Creation Process sets out relevant policy and legislation supporting the BNG approach and a summary of the biodiversity network creation process underpinning the Local Plan.

Dartmoor National Park Natural Environment Topic Paper 2020

Dartmoor National Park Local Plan Topic Paper 1: Natural Environment sets out national policy and legislation relevant to BNG (as at August 2020) and the difficulty in setting BNG policy in this interim period. It then justifies that policy needs to cover: the development threshold above which net gain will be sought; the preference of delivery to be: on-site, then off-site, then as contribution in-lieu and only allowing a less preferential delivery route where a more preferential option is not possible or that evidence demonstrates the contribution will deliver greater environmental benefit; that Natural England’s Biodiversity net gain metric will be used to calculate enhancements; and the minimum maintenance period expected for enhancements. Includes recommendations for bespoke enhancements for minor development.

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 nine authorities set to require developers to provide a biodiversity net gain of over ten per cent and Carter Jonas study on Biodiversity Net Gain in local plans.

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.

We will share further examples of Local Plan evidence and viability assessments for BNG as part of this project.