Biodiversity Net Gain (BNG): frequently asked questions

What is Biodiversity Net Gain?

Biodiversity Net Gain (BNG) is a mandatory requirement (with limited exemptions) for planning permissions granted in England under the Town and Country Planning Act 1990 (TCPA 1990).

BNG aims to ensure all developments have a positive impact on biodiversity. How is this measured? The biodiversity value of a site is assessed before and after development, with developers required to hit a net gain of at least 10%.

The term can also be used to refer to policy-based BNG requirements of local authorities where they are included in local plans.

When does it come into force?

The mandatory BNG requirement (subject to limited exemptions) came into effect on 12 February 2024 for major developments, and 2 April 2024 for small developments.

For the purposes of BNG requirements, a major development includes applications for 10 or more homes or where the application site is half a hectare of larger (full details can be found here). A small development is regarded as anything else.

Nationally significant infrastructure projects will be expected to take BNG into account from late November 2025.

Do I have to consider this for every application?

Not necessarily - there are specific exemptions found in the TCPA 1990 here.

What BNG-specific information do I need to submit with a planning application?

In England, applications for planning permission in England now must be accompanied with additional information including pre-development biodiversity value of the site and details of the calculation, details of any on-site habitats including irreplaceable habitats, and details of any works carried out before the application date that may have degraded the biodiversity value of the application site. 

If you believe BNG does not apply to your application, you must now include a statement highlighting why BNG does not apply to this particular application.

How is biodiversity net gain secured?

Where BNG applies to a planning application and the development is not exempt, any planning permission granted should contain a condition referred to as the 'biodiversity gain condition'.

This requires a biodiversity gain plan to be submitted and signed off by the local planning authority before development begins.

Phased planning permissions should contain a condition requiring an Overall Biodiversity Gain Plan to be submitted and approved before any development begins, with a Phase Biodiversity Gain Plan also needing sign off before development of a particular phase of a development can begin.

Developers should note that even if the local planning authority fails to impose the biodiversity gain condition, under legislation the planning permission will be deemed to have been granted subject to the condition.

Are existing planning applications affected?

If a planning application was made before 12 February 2024 the development is exempt from mandatory BNG.

However, Developers should be aware local planning polices may require a development to deliver BNG.

For example - despite the planning application being made before 12 February 2024, an Inspector dismissed an appeal relating to a proposed development in Northwick for various reasons, including the failure to not deliver BNG under local planning policies.

The inspector noted the requirement under Paragraph 180 of the National Planning Policy Framework which states development should 'contribute to and enhance the local environment in a number of ways, including provision of net gain in biodiversity'.

Curious to read the full decision? The appeal decision can be accessed here.

What if I want to vary an existing planning permission?

Applications to vary existing permissions under the TCPA 1990 will be subject to mandatory BNG requirements if the application to which it relates was made on or after 12 February 2024.

Developers should note it is not possible to vary or remove a statutory planning condition that relates to biodiversity gain. 

Does BNG apply UK-wide?

The BNG requirements found in the TCPA 1990 only apply to planning permissions granted in England.

How do I measure biodiversity?

The value of any habitat or habitat enhancement are calculated using the statutory biodiversity metric.

This is a calculator published by the Secretary of State that must be used by a competent person to figure out biodiversity value for the purposes of biodiversity net gain, calculating existing habitats, habitat enhancements and habitat creation in habitat units (area habitat units, hedgerow units and/or watercourse units).

Do I have to deliver more than 10% BNG?

The requirement is to deliver 'at least' 10% - Whilst local planning authorities may seek a higher percentage, government guidance is that they should not do so 'unless justified'.

Where does BNG have to be delivered?

A development's biodiversity value is figured out from the post-development value of on-site development, any registered off-site biodiversity gain allocated to the development, and the value of biodiversity credits purchased for the development.

However, when submitting a biodiversity gain plan, developers must satisfy the local planning authority that they have applied the "Biodiversity Gain Hierarchy".

This Hierarchy contains different rules for habitats of different distinctiveness, but broadly BNG should be secured on-site (either through the creation or enhancement of existing habitats) before looking to off-site BNG being allocated to the development or the purchase of statutory credits.

BNG can therefore be delivered both on-site and off-site, although the biodiversity metric has a multiplier that requires more off-site units or credits to be provided where off-site BNG is outside the local planning authority's area or the National Character Area where the development has been carried out.

This reflects a preference for on-site or local BNG enrichment and looks to incentivise local habitat delivery.

What are on-site and off-site units?

On-site means within the boundary of the development. Where BNG cannot be achieved on a development site alone, off-site units on land other than the development site can be taken into account in deciding whether a development meets biodiversity net gain objectives.

Can I sell biodiversity units?

Yes. Before you can sell biodiversity units, they must be registered on the Biodiversity Gain Site Register.

Registered units can be allocated to one or more developments for which planning permission is granted.

In order to be registered, the landowner of the biodiversity gain site land must have entered into a conservation covenant or planning obligation, which secures the habitat enhancements and their subsequent management and maintenance for at least 30 years after the completion of those works.

What are statutory biodiversity credits?

If a developer is unable to use on-site or off-site units to deliver BNG, as a last resort they must buy statutory biodiversity credits through the credit sales service. Defra has published guidance on how to buy statutory credits and their prices which can be accessed here.

Developers will need to provide evidence that the other options are not available and should get confirmation from the local planning authority that they can use statutory credits before buying them.