Biodiversity net gain (BNG) for development in England

Most planning permissions in England must deliver a biodiversity net gain of at least 10%, measured with the statutory biodiversity metric and secured for 30 years. Mandatory BNG has applied to major development since 12 February 2024 and to smaller sites since 2 April 2024. From 6 August 2026 new rules exempt non-major sites of 0.2 hectares or less, let other minor sites go straight to off-site units, exempt temporary permissions of five years or less and remove the self-build exemption.

Reviewed against official sources on 14 October 2026. 5 minute read. Regulators: Local planning authorities, Natural England, Defra.

At a glance

Who must comply: Applicants for planning permission in England under the Town and Country Planning Act, unless an exemption applies; nationally significant infrastructure projects are due to follow.
Thresholds: 10% net gain in biodiversity units. Since 6 August 2026, non-major developments of 0.2 hectares or less are exempt unless they harm on-site priority habitat.
Next key date: BNG for nationally significant infrastructure projects has been delayed; the government has signalled late 2026, with the date to be confirmed.
Regulator: Local planning authorities approve biodiversity gain plans and enforce; Natural England runs the biodiversity gain site register and sells statutory credits; Defra sets the metric.
Maximum penalty: No approved biodiversity gain plan means development cannot lawfully start; breaching the condition or the 30-year agreement is a planning breach enforceable by notice, prosecution and unlimited fines.
Where to do it: Biodiversity gain plan submitted to the local planning authority; off-site sites registered on Natural England's biodiversity gain site register; statutory credits bought from Natural England.

This probably applies to you if

You are applying for planning permission in England for housing, commercial, industrial, mineral or waste development
Your site is larger than 0.2 hectares, or is major development (10 or more homes, 1,000 m² or more of floorspace, or a site of 1 hectare or more)
Your scheme affects priority habitat, however small the site
You own land and want to sell biodiversity units to developers
You are promoting a nationally significant infrastructure project that will fall under BNG when it commences

What BNG requires

Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021, makes every planning permission in England subject to a general condition that the development must deliver a biodiversity gain of at least 10% over the pre-development baseline, measured in biodiversity units using the statutory biodiversity metric (or the small sites metric for smaller schemes). Development cannot start until the local planning authority has approved a biodiversity gain plan showing how the gain will be achieved. Habitat created or enhanced must be secured and managed for at least 30 years through a planning condition, a section 106 agreement or a conservation covenant.

Mandatory BNG commenced on 12 February 2024 for major development and 2 April 2024 for small sites.

The changes from 6 August 2026

The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 (SI 2026/790) apply to applications made on or after 6 August 2026 (and to section 73 variations where the original application was made after that date):

Change	Effect
Small sites exemption	Non-major development on sites of 0.2 hectares or less is exempt, unless it negatively affects on-site priority habitat
Temporary permissions	Development to be reinstated within five years or less is exempt, subject to the same priority habitat test
Minor development hierarchy	Non-major schemes that are not exempt can go straight to off-site units without first showing on-site enhancement is not achievable
Self-build and custom build	The specific exemption is removed; most such homes now fall within the small sites exemption instead

Applications submitted before 6 August 2026 stay under the previous rules. Defra consulted separately on a targeted exemption for some residential brownfield development (closed 10 June 2026) and has promised exemptions for development whose purpose is to conserve biodiversity or to improve parks and playing fields, plus changes to the metric; none of these is yet law.

Existing exemptions

BNG does not apply to householder applications, development that affects habitat below a de minimis threshold (now superseded for small sites by the 0.2 hectare rule), biodiversity gain sites themselves, urgent Crown development, and permissions granted under some permitted development rights. Irreplaceable habitats such as ancient woodland are outside the 10% calculation and need bespoke compensation. Nationally significant infrastructure projects under the Planning Act 2008 are not yet covered; their start date has been delayed and should be confirmed by the government in due course.

The gain hierarchy: on-site, off-site and credits

For major development the plan must follow the gain hierarchy: avoid and minimise impacts, then enhance on site, then use off-site units bought from a registered habitat bank or another landowner's site, and only as a last resort buy statutory biodiversity credits from Natural England. Credits are priced to be more expensive than the market so that they do not undercut habitat creation; the lowest tier starts at tens of thousands of pounds per unit and rises steeply for rarer habitats, and the price list is published by Natural England. Off-site units must come from sites recorded on the biodiversity gain site register, which Natural England runs, and both the gain plan and any allocation of units are checked by the planning authority.

How to comply, step by step

Check whether an exemption applies
Measure the site area and confirm whether it is major development; check for priority habitat; note the application date against 6 August 2026.
Survey and baseline the site
An ecologist records habitat types, condition and area and calculates baseline units in the statutory metric (or small sites metric).
Design for net gain
Apply the hierarchy: avoid losses, enhance on site, then source off-site units or credits for any shortfall. Allow for the spatial and temporal multipliers in the metric.
Submit the biodiversity gain plan
After permission is granted and before commencement, submit the plan with the metric calculation, habitat management and monitoring plan, and evidence of off-site allocations or credit purchase.
Secure 30 years of management
Through condition, section 106 agreement or conservation covenant, with a funded management and monitoring regime and reporting to the authority.

Wales, Scotland and Northern Ireland

Mandatory BNG is an England-only regime. Wales requires a "net benefit for biodiversity" through Planning Policy Wales and the section 6 biodiversity duty in the Environment (Wales) Act 2016, assessed through the DECCA framework rather than a metric. Scotland requires developments to deliver positive effects for biodiversity under NPF4 Policy 3, with proportionate enhancement for smaller schemes and no mandatory metric. Northern Ireland relies on planning policy and the Wildlife and Natural Environment Act duties, with no statutory net gain requirement.

Enforcement

Starting development without an approved biodiversity gain plan breaches the planning permission, and failing to deliver the habitat or the 30-year management breaches the condition and the legal agreement. Planning authorities can serve enforcement and breach of condition notices and prosecute, with unlimited fines on conviction, and can enforce the conservation covenant or section 106 obligations directly. Because the gain plan and register are public, failures are easy to identify.

How it differs across the UK

E England: Mandatory 10% BNG under Schedule 7A since February and April 2024, with the 6 August 2026 exemptions and hierarchy changes; NSIPs to follow.
W Wales: No mandatory metric-based BNG; developments must show a net benefit for biodiversity under Planning Policy Wales and the Environment (Wales) Act 2016 section 6 duty.
S Scotland: NPF4 Policy 3 requires development to enhance biodiversity, with significant positive effects for major developments, assessed through planning rather than a statutory metric.
NI Northern Ireland: No statutory net gain requirement; biodiversity is addressed through planning policy and the Wildlife and Natural Environment Act (Northern Ireland) 2011 duties.

Key dates

6 Aug 2026

BNG changes take effect: 0.2 hectare small sites exemption, temporary permissions exemption, minor development hierarchy, self-build exemption removed

Planning applicants in England (applications made from this date) E
Q4 2026

Biodiversity net gain expected to extend to nationally significant infrastructure projects (date to be confirmed)

NSIP promoters E Proposed
2027

Further proposed BNG changes: brownfield exemption, conservation and parks exemptions, metric changes

Planning applicants in England E Proposed

Dates marked “Proposed” are announced or consulted on but not yet law. See the full deadlines calendar.

Penalties and enforcement

Breach	Penalty	Applies in
Commencing development without an approved biodiversity gain plan, or failing to deliver the secured habitat	Breach of planning control: enforcement notice, breach of condition notice, prosecution with an unlimited fine; enforcement of the section 106 agreement or conservation covenant	E	Source

Compliance checklist

Site area and major/non-major status checked against the 0.2 hectare exemption and 6 August 2026 transition
Priority habitat presence confirmed by an ecologist
Baseline and post-development units calculated in the statutory metric
Gain hierarchy applied and off-site units or credits sourced for any shortfall
Biodiversity gain plan approved before commencement
30-year habitat management and monitoring plan funded and secured
Off-site sites confirmed on the biodiversity gain site register

Where to do it: official services

Biodiversity net gain: guidance collection Guidance
Who must deliver BNG, exemptions, the metric, gain plans and the register. Defra and Natural England via GOV.UK E
Statutory biodiversity metric tools and guides Tool or calculator
Download the statutory metric and small sites metric calculators. Natural England E
Register a biodiversity gain site Register or apply
Add land to the biodiversity gain site register so its units can be allocated to developments. Natural England E
Buy statutory biodiversity credits Pay
Current credit prices and how to buy credits as a last resort. Natural England E
Biodiversity gain plan template Report or submit
The form submitted to the planning authority before development starts. Defra E

The law behind this

Questions people ask

Are small developments exempt from biodiversity net gain?

Since 6 August 2026, non-major development on a site of 0.2 hectares or less is exempt from mandatory BNG, provided it does not negatively affect priority habitat on the site. Larger minor developments must still deliver 10% but can go straight to off-site units. Applications made before 6 August 2026 remain under the earlier rules, which exempted only very small habitat losses.

Does BNG apply to self-build homes?

The dedicated self-build and custom-build exemption was removed on 6 August 2026. Most self-build plots are under 0.2 hectares and so fall within the new small sites exemption instead, but a larger plot, or one affecting priority habitat, must deliver 10% net gain.

How much do biodiversity units and credits cost?

Off-site units are sold by habitat banks and landowners at market prices that vary by habitat type and location, commonly in the tens of thousands of pounds per unit. Statutory credits from Natural England are deliberately priced above the market, starting at tens of thousands of pounds for the lowest-distinctiveness habitats and rising steeply for rarer ones; Natural England publishes the current price list.

When does BNG apply to nationally significant infrastructure projects?

Not yet. The government has delayed the start of BNG for NSIPs under the Planning Act 2008 and has signalled a date in late 2026, but it has not been fixed in regulations. Promoters should design for net gain now and check the latest GOV.UK guidance for the commencement date.

What happens if we start work without an approved biodiversity gain plan?

Development is unlawful until the plan is approved, so starting early is a breach of planning control. The authority can serve a breach of condition or enforcement notice, prosecute with unlimited fines, and require the habitat to be delivered. Allow at least eight weeks after permission for the authority to determine the plan.

Does biodiversity net gain apply in Wales or Scotland?

Not as a mandatory 10% metric requirement. Wales requires a net benefit for biodiversity through planning policy and the Environment (Wales) Act duty; Scotland's NPF4 requires developments to enhance biodiversity, with significant positive effects for major schemes. Both can require ecological surveys and enhancement, but without England's statutory metric, gain plan and 30-year rules.

Terms used in this guide

Biodiversity unit: The measure of habitat value in the statutory metric, combining area, distinctiveness, condition and strategic significance.
Statutory biodiversity metric: Defra's calculation tool for measuring biodiversity units before and after development; a simplified small sites metric exists for smaller schemes.
Biodiversity gain plan: The document approved by the planning authority before development starts, showing how the 10% gain will be delivered and secured.
Biodiversity gain site register: Natural England's public register of land where off-site habitat is created or enhanced for allocation to developments.
Statutory biodiversity credits: Credits sold by Natural England as a last resort where on-site and off-site gains cannot be achieved, priced above the market.
Priority habitat: Habitats of principal importance listed under section 41 of the NERC Act 2006; harming them removes the benefit of the new small sites exemption.

Full glossary

Sources

Reviewed 14 October 2026. If you spot something out of date, email info@thamesenvironment.com.