Biodiversity Net Gain (BNG)

Since 2024, most planning permissions in England have carried a condition you cannot negotiate away: the development must leave biodiversity at least 10% better than it found it, and keep it that way for thirty years. It is measured, not asserted. There is a metric, there are units, and a plan has to be approved before you can lawfully start. This page explains how it works, who is exempt, and what changed on 6th August 2026.

NSIPs: mandatory BNG is being extended to nationally significant infrastructure projects from 2nd November 2026. See our practitioner update on NSIP biodiversity net gain and what promoters need to prepare before the new regime starts.

 

 

What is biodiversity net gain?

Biodiversity net gain comes from Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. Every grant of planning permission in England is deemed to have been granted subject to a general condition: a biodiversity gain plan must be submitted and approved by the authority before development can lawfully begin.

The plan has to show that the biodiversity value after development exceeds the pre-development value by at least 10%, measured using Defra’s statutory biodiversity metric and expressed in biodiversity units. Where a Local Nature Recovery Strategy (LNRS) has been published, its mapped priorities can also matter to the metric’s strategic-significance element. Off-site gains and significant on-site habitat enhancements must be secured and maintained for at least 30 years. Significant on-site gains can be secured by a planning condition, a section 106 agreement or a conservation covenant. Non-significant on-site enhancements do not normally carry the same 30-year maintenance requirement.

It became mandatory for major development on 12th February 2024, and for small sites on 2nd April 2024.

What makes it different from the rest of environmental planning is that it is measurable. The mitigation hierarchy in national policy asks you to avoid, minimise, mitigate and then compensate. BNG sits on top of that and adds a number. Designated sites, irreplaceable habitats and protected species keep every protection they already had. If protected species may be present, our ecological survey calendar explains the main seasonal survey windows.

How the 10% is delivered

There are three routes, and until now they ranked strictly in order of preference:

• on-site: habitat created or enhanced within the red line
• off-site: registered biodiversity gain allocated to the development
• statutory biodiversity credits: bought from the government, and a genuine last resort

This changed for smaller schemes on 6th August 2026. For development that is not major development, on-site enhancement, on-site creation and registered off-site gain all sit at the same level of preference. You no longer have to exhaust the on-site options before looking off-site. Credits remain the last resort.

For major development the hierarchy is unchanged: on-site first.

That is a meaningful relaxation for small developers, who often had no realistic way of squeezing a 10% uplift onto a tight site and were being pushed towards credits.

Watercourse projects can work differently. The June 2026 statutory metric guidance expressly recognises fish-passage improvements. Our fish pass planning permission guide explains how that sits alongside planning, Environment Agency and heritage consents. Features introduced to restore natural river function or improve migratory pathways, including an in-river fish pass such as a rock ramp, should not themselves be recorded as watercourse encroachment. Where a technical fish pass attached to an existing weir is the only feasible enhancement option, the existing weir’s encroachment multiplier may be reduced from major to minor in the enhancement calculation. That can make a fish-pass project part of the BNG solution rather than simply another source of habitat loss. See the current statutory biodiversity metric guidance.

Who is exempt from biodiversity net gain?

Most of the exemptions sit in the Biodiversity Gain Requirements (Exemptions) Regulations 2024. Two of them sit in the Act itself. As things stand they include:

• permitted development, meaning anything granted by a development order rather than by the council. That covers anything you build under permitted development rights, including the classes where you have to ask the council first under prior approval
• de minimis development, which does not impact a priority habitat and affects less than 25 square metres of on-site habitat with a biodiversity value above zero, or less than 5 metres of linear habitat such as a hedgerow
• householder applications, as defined in the Development Management Procedure Order, so most extensions, loft conversions and conservatories
• self-build and custom housebuilding: no more than 9 dwellings on a site no larger than 0.5 hectares, consisting only of self-build or custom housing. But see below: this is being removed
• biodiversity gain sites: land being developed in order to fulfil someone else’s BNG condition
• small development applied for before 2nd April 2024. That was the run-in period while small sites were brought into the scheme, so it is history for anything you apply for now. It still matters though, because a section 73 application to vary one of those permissions stays exempt as well
• urgent Crown development under section 293A
• development forming part of, or ancillary to, the high speed railway network

Separately, there are things the condition simply does not attach to. They are not exemptions in the strict sense, but everybody treats them as exempt and you will see them described that way. Reserved matters approvals are not applications for permission, so the condition sits on the original outline. Permission in principle is outside it, though the technical details consent is not. Retrospective applications under section 73A are outside it. Reviews of old mineral permissions sit outside it for the same reason. And it has not yet been commenced for local development orders, simplified planning zones, neighbourhood development orders, deemed permission or permissions granted on enforcement appeals.

Irreplaceable habitat is a different case again, and it gets called an exemption when it is nothing of the sort. Ancient woodland, lowland fen, coastal sand dunes and the others on the statutory list are treated separately because they cannot realistically be recreated. They are recorded in the metric, but they carry no value towards your 10%, so they will not usually help you meet it. If your development harms them you have to agree a bespoke compensation package with the council on top of the gain plan, and you cannot buy your way out of that with credits. If you are enhancing the habitat, or leaving it alone, no compensation package is needed. National policy is the real hurdle here, not the metric: development that would lose or damage an irreplaceable habitat should be refused unless there are wholly exceptional reasons and a suitable compensation strategy exists.

What changed on 6th August 2026

The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 were made on 9th July 2026 and came into force on 6th August 2026. They are now in effect. They do four things: the three changes to the exemptions below, plus the change to the hierarchy set out further up this page.

1. A new exemption for development no larger than 0.2 hectares. Two conditions, and both must be met:

• the development does not impact an onsite priority habitat
• the site has an area no larger than 0.2 hectares

Read the first condition carefully, because it is where this exemption will be won and lost. A habitat is “impacted” if it is lost or degraded such that there is a decrease in its biodiversity value. A small site with a priority habitat on it gets no exemption however small it is. Priority habitats are those on the government’s published list of habitats of principal importance.

2. A new exemption for temporary development. Three conditions: no impact on an onsite priority habitat; the whole of the development consists solely of temporary development; and the period does not exceed five years. Temporary means the permission carries a condition requiring the buildings to come down, the use to stop and the land to be put back, all inside that five years. There is an anti-avoidance rule: if a fresh permission for the same temporary development takes the total beyond five years, the exemption falls away.

3. The self-build and custom build exemption is removed. This is the one that gets missed in the coverage, because it is a loss rather than a gain. The reasoning is that the new 0.2 hectare rule will catch most small self-build plots anyway, but that is not the same thing. A self-build scheme of up to nine dwellings on up to 0.5 hectares was exempt regardless of habitat. From 6th August, a self-build plot over 0.2 hectares, or with a priority habitat on it, is in the regime.

 

Which rules apply to your application?

The same trap as with planning appeals: the date that matters is the date the application was made. It is not the date the council validated it, and it is not the date it gets decided. That is what the transitional provision in the 2026 regulations turns on.

The transition is tied to the date the application was made. For applications already in the system before 6th August 2026, the pre-change position continues to matter.

• the hierarchy: if the application was made before 6th August 2026, the old strict order still applies, so you have to exhaust the on-site options before looking off-site
• the 0.2 hectare exemption: this is available only where the application for planning permission was made on or after 6th August 2026
• the temporary development exemption: this is also available only where the application for planning permission was made on or after 6th August 2026
• the self-build and custom build exemption: if the application was made before 6th August 2026, that exemption is still available, even though it has gone for new applications

An application made before 6th August 2026 does not pick up the new 0.2 hectare or temporary-development exemptions merely because the council decides it after that date. Keep the application date separate from the validation date and the decision date.

Keep proof of when you submitted. Being made and being validated are not the same thing and the two can be days or weeks apart, so if yours straddles 6th August the submission date is the one to argue from.

For section 73 applications the transitional rules reach further back, and they treat the hierarchy and the self-build exemption separately.

• the hierarchy: the old order of preference still applies to a section 73 application made on or after 6th August 2026 where the application for the original permission was made before that date, or where the original permission was granted before it
• the self-build exemption: if the original permission escaped the biodiversity gain condition under the old self-build rule, a section 73 application made on or after 6th August does not drag the condition back in

There is one neat piece of transitional drafting worth knowing: if the original permission was exempt under the old self-build rule, and you apply under section 73 on or after 6th August, the biodiversity gain condition still does not apply. The removal of the exemption does not reach back and catch schemes that relied on it.

The change to the hierarchy follows the same pattern. The old order of preference still applies to any application made before 6th August 2026, and to a section 73 application made on or after that date where the original permission was applied for, or granted, before it.

 

What you have to submit, and what it costs

If you believe you are exempt, you have to say so on the application form and give your reasons. That is a requirement, not a courtesy, and the council checks it when it validates. Every application already needs a location plan with a red line round the site, and that is what the council will measure the 0.2 hectare exemption against.

Where more than one exemption could apply, you do not have to prove them all. Pick whichever is easiest to demonstrate. The steer is householder first, then the 0.2 hectare rule, then de minimis.

If you are not exempt, the application has to carry a set list of biodiversity net gain information. Leave any of it out and the council will probably refuse to validate:

• confirmation that you accept the biodiversity gain condition will apply
• the pre-development biodiversity value of the site, and the date you have used to work it out
• the completed metric calculation tool showing how you got there
• a statement about whether the site has been degraded, with the earlier value if it has
• a description of any irreplaceable habitat on the land
• scaled plans showing the habitat that is there now, with north marked

The gain plan itself comes later. It cannot be submitted until the day after permission is granted, and the council then has 8 weeks to decide it unless you agree something longer in writing.

There is a fee. Submitting a gain plan counts as asking the council to confirm in writing that a condition has been complied with, so it is charged like any other discharge of conditions request, per request. Current figures are on our planning fees page. If the council takes longer than 12 weeks the planning guarantee applies and the fee has to be refunded.

One thing to watch: there is no way to amend an approved gain plan. If your approach changes before you start, say you switch from off-site units to credits, you have to submit a fresh plan and get that approved instead.

Gain plans are public. The council has to put a copy on the planning register along with its decision.

 

If the council refuses your gain plan

A refusal is not the end of it. You can appeal to the Secretary of State under section 78, exactly as you would against a refusal of permission, and you can appeal in the same way if the council simply fails to decide within its 8 weeks. For applications submitted on or after 1st April 2026, a refusal appeal is eligible for the Part 1 written representations procedure, although the Planning Inspectorate says Biodiversity Gain Plan refusals will usually be moved to Part 2. A non-determination appeal follows Part 2.

The deadline is 6 months, running either from the decision or from the date a decision should have been given. That is much longer than most of the deadlines on our planning appeals page, so do not assume the householder 12 weeks applies here.

Before appealing it is usually quicker to go back to the case officer and ask what would make the plan acceptable. Most refusals turn on missing evidence rather than on principle.

There is one gap. If the Secretary of State was the authority deciding your gain plan and refused it, there is no appeal at all. The only route is a challenge in the High Court within 6 weeks under section 288. The same 6 weeks applies to challenging an appeal decision.

 

If your development is phased

Large schemes granted outline permission, or granted with conditions requiring the work to come forward in phases, are handled differently. Instead of one gain plan you need two kinds:

• an Overall gain plan, approved before anything at all can start, setting out how the 10% will be met across the whole site
• a Phase gain plan for each phase, approved before that phase can start

The 10% is measured against the whole development rather than each phase, so an early phase can contribute less as long as the total lands. The pre-development value is fixed once for the entire site and is not recalculated phase by phase. The same 8 week clock and the same appeal rights apply to both kinds of plan.

The decision notice will say whether the council treats your permission as phased. Not every outline permission is: one where only appearance and landscaping were reserved probably is not.

 

The traps

• “Before you can lawfully begin” means what it says. The gain plan must be approved before development starts. Starting without approval is a breach of the condition, and it may mean your start was not lawful at all, which matters if the permission is running out. See our guide to making planning extant
• Degrading the site first does not help. If biodiversity value was reduced by unauthorised activity after 30th January 2020, the value is assessed as at before those activities. There is an equivalent rule for authorised activities after 25th August 2023
• Priority habitat defeats the small-site exemptions. Both new exemptions fall away if an onsite priority habitat is impacted. On a 0.15 hectare plot with a species-rich hedgerow, the 0.2 hectare rule will not save you
• Your council cannot bolt extra on top. An area-wide local policy asking for more than the statutory minimum, or applying BNG to exempt development, should not be given weight. Under N1 and N2 of the August 2026 NPPF, a higher local standard is limited to a specific site allocation and must be fully justified and deliverable
• 30 years is a long commitment. Off-site gains and significant on-site enhancements must be secured and maintained for at least 30 years, with monitoring. Non-significant on-site enhancements do not normally carry that same statutory maintenance requirement
• Irreplaceable habitat is a separate regime. Ancient woodland and the like are dealt with under their own regulations, and no amount of net gain buys your way through
• BNG does not erase site protection. If a proposal affects a Local Wildlife Site or another protected nature site, the relevant site policy and mitigation hierarchy still apply alongside the metric

 

Recent High Court cases: BNG must be handled transparently

 

Two 2026 High Court judgments are useful reminders that the biodiversity number is only one part of lawful decision-making.

In Greystoke CB Limited v Secretary of State for Communities, Housing and Local Government & Anor [2026] EWHC 1997 (Admin), the Inspector found that a proposed Banbury logistics development would deliver 23% habitat BNG and 10% hedgerow and treeline BNG, but the benefit then disappeared from the final planning balance. On the way the case was argued, the court held that omission was unlawful. The judgment does not establish that every percentage uplift must always receive positive weight; it does show that where BNG is a material consideration which must be taken into account, recording it in one section of a decision and then overlooking it in the balance is not enough.

For the highway and planning-balance issues as well as the BNG point, see our Greystoke High Court news analysis.

Guardians of Whitewebbs Park CIC v London Borough of Enfield [2026] EWHC 1916 (Admin) raises a different warning. Enfield's ecological consultant disputed the claimed BNG of more than 33%, but the committee report presented the Ecology Officer as having no objection. The High Court found the committee had been materially misled and that the failure to make the relevant ecological report available as a background paper had caused material prejudice. The permission was quashed. The court did not decide which ecological calculation was correct; the legal problem was that the genuine technical disagreement was not presented fairly. Our Whitewebbs BNG report case analysis explains the judgment and the committee-report issues in more detail.

The practical point is simple: calculate BNG properly, but also make sure the decision-maker is told what the figure means, what is disputed and what weight is actually being given to it.

 

Is BNG worth designing around?

For anything above the exemption thresholds, you have no choice. But the honest advice is that BNG is far cheaper designed in than bolted on. A scheme laid out to retain a hedgerow and leave a margin can often hit 10% on site for very little. The same scheme drawn to the boundary, with the habitat cleared, ends up buying credits at a price set to be unattractive.

And if you are near a threshold, the numbers matter. A red line at 0.19 hectares is exempt from 6th August. At 0.21 it is not. That is worth knowing before the drawings are finished, not after.

Biodiversity net gain relevant legislation

Biodiversity net gain sits in a schedule to the main planning Act, with the detail spread across four sets of regulations. It is a fast-moving area, so always use the “Changes to Legislation” panel on legislation.gov.uk, as later amendments are not always shown in the main text.

• Town and Country Planning Act 1990, Schedule 7A: the biodiversity gain objective, the general condition and the gain plan
• Environment Act 2021, Schedule 14: inserted Schedule 7A
• Biodiversity Gain Requirements (Exemptions) Regulations 2024 (SI 2024/47): the exemptions
• Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 (SI 2026/790): the 0.2 hectare and temporary development exemptions, the removal of the self-build exemption, and the revised hierarchy, all from 6th August 2026
• Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024 (SI 2024/48): irreplaceable habitat
• Biodiversity Gain (Town and Country Planning) (Modifications and Amendments) (England) Regulations 2024 (SI 2024/50): inserted Part 7A into the Development Management Procedure Order: gain plan form, timing, content, determination and appeals

Other Common Projects

 

 

Conservation, Heritage & Protected Sites

 

 

Biodiversity Net Gain Page Updated: 8th September 2026