BNG Planning: Requirements for Development in England

BNG planning: understand the requirements before you apply

BNG planning requirements affect how many developments in England are designed, submitted and delivered. If you are preparing a biodiversity net gain planning application, you need to distinguish the information required with the application from the biodiversity gain plan approved after permission. Collington Winter Environmental helps applicants understand BNG for planning, coordinate ecological evidence and plan a realistic route through the biodiversity gain condition. Addressing these stages together can prevent a seemingly successful planning permission from becoming difficult to implement.

The starting point is to establish whether mandatory BNG applies. The Environment Act 2021 introduced the framework through Schedule 7A of the Town and Country Planning Act 1990. For development within scope, the biodiversity gain objective is at least a 10% increase in biodiversity value, calculated using the appropriate statutory metric. This is a measurable habitat requirement, not simply a commitment to plant more trees or provide a greener-looking landscape.

When do BNG requirements apply?

Mandatory BNG commenced for major development from 12 February 2024 and for small sites from 2 April 2024, subject to transitional arrangements and exemptions. The relevant application date and planning history matter, particularly where a site already has permission or an applicant proposes to vary conditions. The date on which construction is expected to start does not, by itself, determine whether the original application falls within the regime.

Householder development and qualifying self-build or custom-build schemes are among the exemptions. A carefully evidenced de minimis exemption may apply where the relevant habitat impacts fall below the thresholds and no priority habitat is affected. Permitted development is outside mandatory BNG under this planning framework. Nationally significant infrastructure projects have a separate legislative route and later commencement arrangements; the ordinary planning dates should not be applied to them automatically.

Where an exemption is claimed, the application should explain why it applies and provide supporting information where needed. Being exempt from statutory BNG does not remove protected species legislation, designated site safeguards or relevant local planning policies. Read our guide to whether biodiversity net gain is mandatory before assuming that an ecological assessment is unnecessary.

What does a planning authority need at validation?

National application information

For an application within scope, national requirements include confirmation that the biodiversity gain condition would apply, the pre-development biodiversity value and the completed metric calculation used to establish it. Applicants also need to provide the relevant baseline date and explain an earlier date where one is proposed. The information should be based on a survey and mapped habitats, not a speculative desktop score.

The application must address whether relevant earlier habitat degradation has occurred and whether irreplaceable habitat is present. A plan identifying the on-site habitats existing at the baseline date should support the calculation, with the required plan details. These elements allow the authority to understand the starting point against which biodiversity gain will later be assessed. Missing or inconsistent baseline evidence can create validation problems before the merits of the design are considered.

Local validation lists and supporting detail

Councils may also seek proportionate supporting material through their published local validation requirements. This can include a BNG statement, proposed habitat plans, a draft post-development metric or an explanation of likely off-site provision. Check the relevant authority's requirements rather than assuming that every council uses an identical checklist. Local information requests should be distinguished from the national minimum requirements and the later statutory gain plan.

Even where a final gain plan is not required at application stage, the authority needs enough information to consider whether the proposal can deliver biodiversity gain. A scheme that relies on unrealistic habitat creation or unavailable land may raise substantive planning concerns. For this reason, a baseline-only submission may satisfy some information requirements without resolving the practical questions that matter to determination.

Preparing BNG for planning alongside the design

The habitat baseline should inform the layout rather than follow it as a separate administrative exercise. Retaining established habitats may reduce losses and support a more achievable gain strategy. Landscape, drainage, access and engineering proposals should be reviewed together because their land requirements often overlap. A parcel cannot realistically function as dense woodland, an open visibility splay and a regularly disturbed maintenance corridor at the same time.

Use the biodiversity gain hierarchy to guide decisions about avoidance, mitigation and habitat delivery. Where on-site measures cannot meet the requirement, identify the nature of the remaining shortfall and the likely off-site route early. An outline statement that units will be purchased later is not a substitute for understanding what units are needed and whether the strategy is viable. Our metric calculation service helps translate design options into measurable implications.

Trading rules matter as well as the percentage

The metric separates area habitats, hedgerows and watercourses, with trading rules governing the replacement of habitat losses. A positive overall area-habitat percentage does not necessarily resolve a hedgerow deficit or an unacceptable habitat trade. These distinctions should be checked before the application relies on a headline claim that the development achieves 10%.

The same caution applies to off-site provision. Its location affects the spatial risk multiplier, so the number of units available from a supplier may differ from the number that can count towards your scheme. Discussing these issues during design is generally more useful than discovering a mismatch when the gain plan is ready for submission.

The statutory biodiversity gain condition

Planning permission for development within scope is subject to the statutory biodiversity gain condition. In practical terms, development must not commence until the biodiversity gain plan has been submitted to and approved by the relevant planning authority. The condition operates through legislation; applicants should not assume it disappears if a decision notice does not reproduce it as an ordinary bespoke condition.

The gain plan records how the biodiversity gain objective will be met. It brings together the approved development, the final biodiversity metric, on-site habitat proposals, allocated registered off-site gains and any statutory credits used as a last resort. Application-stage documents should provide a coherent foundation for that later submission rather than promise one strategy and leave another to be devised after permission.

Permission is not the final BNG approval

Receiving planning permission does not mean all BNG obligations have been discharged. Before arranging a start on site, check the status of the gain plan, associated legal arrangements and any separate ecological conditions. Other consents or licences may also be necessary. Starting work prematurely can create enforcement and compliance risks, even where the development has an otherwise valid permission.

Significant on-site habitat enhancements and registered off-site gains require long-term security and management for at least 30 years under the applicable framework. A habitat management and monitoring plan may therefore need to be prepared alongside the gain plan. This should explain the work required, who will undertake it and how progress towards the target habitat condition will be assessed.

BNG planning for small sites

Small developments are not automatically exempt. Where mandatory BNG applies, the Small Sites Metric can simplify assessment for eligible proposals. Residential eligibility generally covers one to nine dwellings on a site smaller than one hectare, or a site smaller than half a hectare where dwelling numbers are not known. Non-residential eligibility has its own floorspace and site-area limits, and ecological exclusions must also be checked against the current metric guidance.

The simplified tool cannot be selected solely because a scheme is described informally as small. Priority habitats, protected sites and relevant protected species constraints can make it unsuitable. A competent person must still establish the habitats and follow the tool's rules. The target remains at least 10%, and a small plot may still need off-site units if it cannot accommodate sufficient suitable habitat.

Planning timelines: build in dependencies, not assumptions

There is no single BNG timetable that fits every site. Habitat survey requirements, design changes, authority queries, legal agreements and off-site availability can all affect progress. Some ecological work is seasonally constrained. Establishing the survey programme before submitting the application helps identify which tasks can run together and which depend on information that is not yet available.

The statutory gain-plan determination period is generally eight weeks from the day after receipt, unless a different period is agreed in writing. That does not guarantee approval within a particular construction programme: an incomplete or inadequate submission can lead to refusal or further work. Allow for preparation and securing delivery arrangements before submission, as well as the authority's assessment period afterwards.

For phased development, additional rules apply to overall and phase-specific gain plans. Outline applications also need an approach that remains workable when detailed design follows. Avoid relying on untested assumptions about what later reserved matters or phases will provide. A clear allocation of responsibilities between the applicant, project ecologist, landscape designer, legal adviser and future land manager helps keep the process coordinated.

Why choose Collington Winter

Based in Bolton, Collington Winter Environmental works throughout England. Olivia Collington, our Managing Director, is a Chartered Environmentalist with the IES and has experience with the DEFRA Statutory Biodiversity Metric and habitat bank offsetting. We help connect planning-stage evidence with the habitat delivery and management needed after permission, rather than treating the calculation as an isolated document.

Explore what BNG means, when assessments are required and habitat banking for further context. To discuss BNG requirements for your planning application, call 01204 939 608 or use our contact page.