Biodiversity Net Gain rules have changed: Is your planning application ready?

For developers, landowners, investors and owner occupiers submitting planning applications, it is important to understand whether one of the new Biodiversity Net Gain exemptions applies to your scheme or whether your development must still deliver the mandatory 10% Biodiversity Net Gain.

While the latest changes are intended to reduce the burden on some smaller schemes, BNG remains an important consideration for development across England, and one which should be addressed from the outset of the planning process.

So, what are the latest BNG exemptions, which developments are exempt and what should you be doing before submitting your next planning application? Sarah Isherwood, Planning Partner at Vail Williams, explains.

What is Biodiversity Net Gain (BNG)?

Biodiversity Net Gain is an approach to development which seeks to leave the natural environment in a measurably better condition than it was beforehand.

Mandatory BNG was introduced in England for most major developments in February 2024 and for small sites from April 2024.

Unless a development is exempt, developers are generally required to deliver a minimum 10% Biodiversity Net Gain, calculated using the statutory biodiversity metric.

The principle is not simply to compensate for habitat lost through development, but to ensure that the overall biodiversity value following development is at least 10% greater than the site’s baseline value.

This means BNG can have implications for site design, development density, viability, land requirements, planning strategy and project timescales.

It is therefore something which developers and landowners should consider at an early stage, not once a planning application is ready for submission.

Which developments are exempt from Biodiversity Net Gain?

Not every planning application is subject to mandatory BNG.

Following the changes introduced on 6 August 2026, qualifying development on sites with a red line boundary of 0.2 hectares or less may benefit from a Biodiversity Net Gain exemption, as can certain temporary developments where planning permission is granted for no more than five years.

Other BNG exemptions also exist within the regime.

It is important, therefore, not to assume that BNG either does or does not apply based solely on the size or nature of a development.

Particular care is needed where priority habitat could be affected, since this can prevent a development from benefiting from the new small-site or temporary development exemptions.

Establishing whether an exemption applies should be one of the first considerations when preparing your planning strategy.

What does the 10% Biodiversity Net Gain requirement mean?

Where your development is not exempt from mandatory BNG, you will generally need to demonstrate how it will achieve at least 10% Biodiversity Net Gain.

The starting point is understanding the existing biodiversity value of the site.

This is assessed using the statutory biodiversity metric, which compares the site’s pre-development biodiversity value with its proposed post-development value.

The calculation takes account of factors such as the type, size, condition and strategic significance of habitats. This means the implications of BNG can vary significantly from one development site to another.

Carrying out the necessary BNG assessment at an early stage can help developers establish the biodiversity baseline, identify potential constraints and understand how the 10% requirement could affect the proposed scheme.

How can developers achieve 10% BNG?

There are three principal ways in which the required biodiversity gain can be delivered.

On-site BNG involves creating or enhancing habitats within the development’s red line boundary.

Off-site BNG involves securing registered biodiversity gains elsewhere, either on land controlled by the developer or through the purchase of biodiversity units from another landowner.

Statutory biodiversity credits can be purchased from Government as a last resort where the necessary gain cannot be secured through on-site or off-site provision.

For most developments, significant on-site habitat enhancements and off-site gains must be secured and maintained for at least 30 years.

The most appropriate solution will depend on the characteristics of the site, the development proposed and the wider commercial and planning strategy.

What do developers and landowners need to do before submitting a planning application?

The most important step is to consider BNG early in the planning process.

Do not wait until your planning application is ready for submission to establish whether BNG applies or how you are going to achieve it.

Before progressing an application, developers and landowners should consider:

• Whether the proposed development is subject to mandatory BNG or qualifies for a BNG exemption.
• Whether priority habitat is present which could affect the ability to rely on an exemption.
• The site’s existing biodiversity value and how the proposed development will affect it.
• Whether the required biodiversity gain can realistically be delivered within the site.
• Whether off-site biodiversity units may be required and the potential cost implications.
• How BNG could affect development design, density, viability and programme.
• What information will need to accompany the planning application.
• What will subsequently be required through the Biodiversity Gain Plan.

Where BNG applies, specified biodiversity information will need to be provided as part of the planning process.

What is a Biodiversity Gain Plan?

Following the grant of planning permission, a Biodiversity Gain Plan will generally need to be submitted to and approved by the local planning authority before development can commence where mandatory BNG applies.

The plan sets out how the development will achieve the required Biodiversity Net Gain, including the measures being used to deliver the necessary biodiversity units.

It therefore forms an important part of the BNG planning process and should be considered alongside the wider planning, design and viability strategy for the site.

Addressing these issues early can help reduce the risk of redesign, unexpected costs and delays later in the planning process.

Are further Biodiversity Net Gain changes coming?

Potentially.

The BNG framework continues to evolve, with Government having consulted on further changes to the regime.

These have included potential additional exemptions and changes to the way BNG is calculated, as well as proposals relating to certain residential development on brownfield land. *The Government’s consultation on a potential targeted residential brownfield exemption closed on 10 June 2026 and is still being considered.

Developers, investors and landowners should therefore keep the position under review when bringing sites forward, rather than relying on their understanding of the BNG regime from an earlier planning application.

Need help with Biodiversity Net Gain and your planning application?

The changes introduced on 6 August will simplify the position for some smaller developments, but they also make it important to establish exactly which Biodiversity Net Gain rules and exemptions apply to your scheme before progressing through the planning process.

Whether you are a developer, landowner, investor or owner occupier, early consideration of BNG can help you understand the planning, design, cost and viability implications of your proposals and identify the most appropriate route to securing planning permission.

If you are preparing a planning application and are unsure whether the Biodiversity Net Gain requirements or exemptions apply, speak to our planning experts. Vail Williams can help you understand the latest BNG rules and exemptions and consider their implications for your site, development strategy and planning application. Get in touch for more information.