Mandatory Biodiversity Net Gain FAQs

Government's Biodiversity Net Gain (BNG) mandate came into force on Monday, 12 February, requiring a minimum of 10% BNG on new major sites in England. 

While the intention of the mandate aligns with home builders' ongoing efforts to protect and enhance natural environments, the impact on an already complex planning system mustn't be overlooked. Delays securing planning consent are already considered a significant barrier to the delivery of much-needed homes - with 93% of SME home builders identifying planning delays as a major barrier to growth.

Local Authorities need to ensure there is sufficient capacity in their teams to process BNG effectively or we will see further delays in the planning process.

As of 1pm on 12 February 2024, some updated guidance is yet to be published, including further advice on how BNG works for phased developments. The Home Builders Federation continues to liaise with Defra and the Department of Levelling Up, Housing and Communities and will update members once this documentation becomes available.

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Biodiversity Net Gain FAQs

Biodiversity Net Gain (BNG) is now a lawful part of the planning system. Planning applications need to set out how a minimum of 10% BNG will be delivered and secured for at least 30 years.

Whilst BNG presents some operational challenges, certainly in the short-term, it has largely been welcomed as a positive step for wildlife and an opportunity for housebuilders to demonstrate that new homes and environment benefits can be delivered together.

BNG for major applications became mandatory on 12 February 2024. BNG for minor applications becomes mandatory on 2 April 2024.

Some types of applications are exempt from BNG requirements. Click here for details.

BNG will not apply to applications submitted before these dates or to reserved matters pursuant to approved outline applications (where the outline was approved prior to 12 February 2024).

Planning Practice Guidance (PPG) is available here.

DEFRA has published guidance on a wide range of BNG implementation issues, click here.

Both the PPG and the DEFRA guidance are expected to be kept under review and evolve further as the practicalities of dealing with BNG become clear.

Sources of More Information

Government guidance:


For developers:

For landowners and brokers:

The Planning Advisory Service (PAS) has been working with LPAs to help them prepare for the implementation of BNG. It’s FAQs is available here.

PAS has posted four ‘toolkit’ videos online, the first of which can be viewed here.

BNG is calculated using statutory biodiversity metric and delivered in accordance with a BNG Plan.

Planning applications submitted after 12 February 2024 will need to use the latest version of statutory metric, transferring into it any information from previous versions that may have been used during pre-application preparation. DEFRA has provided advice on how to do this.

The small sites metric (SSM) will only technically become a statutory metric on 2 April 2024, but should still be used in the interim.

The national statutory metric considers not only the type of the biodiversity asset, but also its condition and rarity. The metric requires any lost biodiversity to be replaced with either a like-for-like asset(s) or one of a better quality. It is not possible to ‘trade down’. The metric also incentivises the implementation of BNG closest to the site, through the multipliers applied to off-site provision and the deliberately high cost of statutory credits.

The statutory metric must be completed by an ecologist.

The small site metric (SSM) does not include an off-site site. It can be used to calculate on-site gains. If any off-site units are required, the Biodiversity Gain Plan will need to summarise how the BNG requirement has been met. The SSM must be completed by a ‘competent person’, but this does not have to be an ecologist.

It is important that BNG is considered at the earliest opportunity. Although technically BNG is a post-development condition, and a BNG Plan can only be submitted and approved after planning permission has been granted, early discussions around BNG and the sharing with a LPA of a draft BNG Plan is very much encouraged.

From 12 February 2024 major applications will need to either include a statement that the application is not subject to mandatory BNG and the reasons why not (i.e. which of the exemptions applies), or a statement that the application is subject to mandatory BNG, accompanied by:

  • the completed metric tool(s) showing the onsite habit score as of the date of the application or an earlier agreed date;
  • if any habitat degradation has occurred, the completed metric for before the degradation occurred;
  • the score in biodiversity units;
  • the publication date of the version of the metric being used (the current version's publication date is 29 November 2023);
  • if any earlier calculation date has been agreed, why it was proposed
  • if any degradation has occurred, a statement that it has occurred, when it started and any evidence for the date it started and the score before the degradation; and
  • a description of any irreplaceable habitat within the red line boundary as of the metric calculation date; and a scale plan of the onsite habitat used in the calculations and any irreplaceable habitat.

The guidance seeks to discourage the deliberate degradation of habitat in order to lower biodiversity metric scores.

If any onsite score-lowering activity that is not part of implementing a planning permission has taken place since 30 January 2020, or that is part of a not-yet-fully-implemented planning permission has taken place since 25 August 2023, then it is to be ignored, and the score is the highest score that can be assumed before that happened reasonably supported by evidence.

The BNG mitigation hierarchy seeks in the first instance to minimise biodiversity loss, but where net gain is required the process allows for on-site biodiversity, off-site biodiversity (which must be registered) and, as a last resort, the purchase of statutory credits.

The regulations set out a 'biodiversity gain hierarchy' of the preferred order of steps that should be followed, which are as follows:

  • Avoid impacts on onsite habitats of distinctiveness at least;
  • Mitigate impacts on such habitats;
  • Compensate through enhancement of onsite habitat;
  • Compensate through creation of onsite habitat;
  • Compensate through allocation of offsite habitat; and
  • Purchase biodiversity credits.

If a developer is able to show that BNG on-site delivery is not desirable and/or deliverable, and that there is no off-site provision available, statutory BNG credits can be purchased.

On-site provision should be explored in the first instance, but there will be instances when on-site BNG is neither possible or desirable. This could relate to site-specific deliverability or suitable, or opportunities (perhaps by way of a Local Nature Recovery Strategy) to coordinate off-site contributions from a number of sites.

If BNG is provided off-site its value in units for a development may be reduced depending how far away it is.

The basic rule is that if the off-site land is anywhere in the same local authority area (district or unitary level) or 'National Character Area (NCA)' then the score does not change.

If though it is in an adjacent local authority or NCA, the score is multiplied by 3/4, and if it is anywhere else in England, it is multiplied by 1/2. So if you are losing four units through the development, you will need to find at least 4.4 units in the same local authority or NCA, 5.87 units in a neighbouring one, or 8.8 units anywhere else.

The regulations state that the BNG Plan (that must be approved before development can commence) must give reasons for not following the order of priority.

Additional DLUHC Guidance on phased development is still awaited.

This will be set out in the legal agreement, click here.

It is possible to buy off-site units from a land manager, the land manager would then be responsible for delivering the BNG in accordance with their legal agreement. It is also possible to make off-site gains on land owned by a developer outside the development site. A legal agreement would need to be in place to secure management of the land for the required 30 years.

On-site gains must last for at least 30 years from the date of completion of the whole development.

Off-site gains must last for at least 30 years from the date the habitat enhancement is finished.

A local plan policy that sought to, for example, ensure that all BNG to be secured was on land within a LPA’s administrative boundary would be unsound and not reflective of how the BNG is expected to work in practice.

Moving forward Local Plan should link into Local Nature Recovery Strategies as these are prepared.

The market for off-site biodiversity provision is still emerging and habitat banks are not yet in place across the whole country.

Future Homes Hub hosts a BNG Unit Finder Map to help match sellers of BNG units with potential buyers.

A national register for net gain delivery sites is being established and all off-site BNG must be registered on it.

Government guidance is clear that viability is not a justification for providing less than the mandatory 10% BNG.

A site-specific viability assessments could though show the impact of BNG on a scheme’s ability to provide other planning gain contributions.

As the market for off-site BNG credits is still emerging costs are not fully known at this time.

The costs of statutory credits has been set out here but it must be remembered that these are set intentionally high to encourage on-site and off-site delivery rather than a reliance on the national credit scheme.

Planning applications where BNG is an issue can be appealed in the usual way.

It is also possible to appeal a refusal of a Biodiversity Gain Plan, and to appeal for non-determination of the Biodiversity Gain Plan if a decision is not made within 8 weeks, or an agreed extended deadline.

Some LPAs already have a BNG policy in an adopted local plan. Where these refer simply to no net loss of biodiversity they will be superseded by the national mandatory requirement.

Some LPAs, Guildford and Cornwall, for example, have policies seeking 20% BNG.

HBF is arguing that any policy looking to go beyond 10% mandatory BNG needs to be robustly evidenced and the costs specifically identified and included within a viability assessment of the whole plan.

Where there is no policy the national requirement will be applied from the relevant date.

If you have any further questions related to BNG, contact the HBF Planning team.

Biodiversity Net Gain Resources

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To access resources related to BNG please sign in to your free HBF account using your work email address. If you haven't yet set up your account but are part of a HBF member organisation you can create an account using your work email address.

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