Comply with biodiversity net gain for development in England

Mandatory biodiversity net gain (BNG) has applied to most planning applications in England since February 2024. You must demonstrate that your development leaves biodiversity in a measurably better state than before — a minimum 10% improvement in biodiversity value, maintained for at least 30 years.

BNG is a planning condition, not a voluntary standard. Your local planning authority (LPA) will not discharge the BNG planning condition until you have submitted and agreed a biodiversity gain plan showing how you will achieve and maintain the 10% improvement.

When mandatory BNG applies

BNG is mandatory for:

• Major developments (10 or more dwellings, 1,000 sqm or more of floorspace, or a site of 1 hectare or more) — from 12 February 2024
• Small sites (1 to 9 dwellings, or sites under 1 hectare that are not major) — from 2 April 2024
• Nationally Significant Infrastructure Projects (NSIPs) — for applications submitted on or after 2 November 2026 (enabling provisions in force from 7 May 2026)

Exemptions

BNG does not apply to:

• Householder applications (extensions and alterations to existing dwellings)
• Single self-build or custom-build dwellings
• Developments with de minimis habitat impact (under 25 square metres of habitat and under 5 metres of linear feature such as hedgerow, where no onsite priority habitat is affected)
• Biodiversity gain sites; urgent Crown or defence development; and high-speed rail (HS2) development
• Development that does not require an application for planning permission

If you believe an exemption applies, you must still submit evidence to your LPA at the time of the planning application. The brownfield exemption was removed — BNG applies to brownfield sites.

Upcoming change: On 15 April 2026 the government confirmed a small-sites exemption for development sites of 0.2 hectares or less, except where priority habitat is affected. It is expected to take effect from end July 2026. Until it comes into force, small sites remain subject to mandatory BNG as set out above.

Step 1: Commission a baseline habitat survey

Before you can calculate BNG, a qualified ecologist must survey and map all habitats on your site using the UK Habitat Classification (UKHab). The survey must be carried out within 2 years before you submit your planning application. The ecologist will assess the type, condition, and strategic significance of each habitat parcel.

Engage an ecologist early — ideally during pre-application discussions with your LPA. Survey findings can influence site layout to protect high-value habitats and reduce the BNG burden.

Step 2: Calculate your biodiversity gain plan

Your ecologist uses the statutory biodiversity metric (version 4.0) to calculate baseline biodiversity units and post-development biodiversity units. The difference must be at least 10% in your favour. You must submit the completed metric and a biodiversity gain plan with your planning application, or by the date set in the BNG planning condition.

The metric uses three types of biodiversity unit: area habitats, hedgerow units, and watercourse units. You must achieve 10% net gain across each type independently — you cannot use surplus hedgerow units to offset a deficit in area habitats.

Step 3: Deliver the required biodiversity units

You must deliver BNG following the statutory hierarchy — on-site first, then off-site, with statutory credits only as a last resort. You will need to demonstrate to your LPA why you cannot achieve the full 10% on-site before using off-site units or credits.

If you use off-site units, the habitat bank site must be registered on the Natural England biodiversity gain site register before your LPA discharges the BNG planning condition. You cannot discharge the condition until registration is confirmed.

Statutory credits are purchased directly from Natural England. They are significantly more expensive than on-site or off-site delivery and are intended to be a last resort — not a convenient shortcut. Revenue from credit sales funds habitat creation elsewhere in England.

Step 4: Secure 30-year habitat management

Every development subject to BNG must have a habitat management and monitoring plan (HMMP) secured through a planning condition, Section 106 agreement, or conservation covenant. The HMMP legally commits the landowner — and any future owner — to managing and monitoring habitats for at least 30 years.

The management obligation transfers with the land. If you sell the site, the buyer takes on the HMMP obligations. Build the 30-year management cost into your development appraisal. For larger schemes, consider using a specialist habitat management company or transferring management to a local wildlife trust.

What happens if you do not comply

Failure to comply with BNG obligations is a breach of planning condition. Your LPA can issue an enforcement notice requiring you to provide alternative or additional habitat. There is no direct financial penalty fixed by statute, but continued breach can result in injunctions, stop notices, and prosecution in the magistrates' court.