What a biodiversity gain plan must contain

A biodiversity gain plan is the document that releases the deemed condition sitting on most planning permissions in England, and it is rejected more often than developers expect. The biodiversity gain plan contents are prescribed rather than discretionary: the steps taken to avoid and minimise harm on site, the pre-development biodiversity value with the date it was fixed, the post-development value, any off-site gains allocated from the register, any statutory credits bought, and a completed statutory metric calculation behind all of it. Get one element wrong and development cannot lawfully begin, because the condition is not discharged.

Where the plan requirement comes from

Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021, places a deemed condition on most planning permissions. The effect is that development may not begin until a biodiversity gain plan has been submitted to and approved by the planning authority.

The regime began on 12 February 2024 for major development and 2 April 2024 for small sites. Several sets of 2024 regulations fill in the detail, covering modifications to the 1990 Act, the exemptions, and the biodiversity gain sites register.

The condition is not the plan. The condition is deemed into the permission automatically, and the plan is the thing you submit to satisfy it. That distinction matters when a scheme is sold on with permission, because the obligation travels with the land and the buyer inherits the problem of a baseline that was never recorded.

A handful of permissions escape the condition. Householder applications, development below the de minimis threshold of 25 m² of on-site habitat and 5 m of linear habitat, qualifying self-build and custom housebuilding of no more than nine dwellings on a site of no more than half a hectare, and development on a registered biodiversity gain site are the ones most often relied on. Each exemption has conditions attached, so read the current regulations rather than a summary.

The pre-development value and the date it is fixed

The pre-development biodiversity value is the single number everything else hangs from, and it is assessed as at a fixed date rather than as at the date you start work.

The default date is the date the planning application was made. The applicant and the authority can agree an earlier date, which is sometimes useful where survey work was done well before submission. Where a planning permission is granted on an application that did not record a baseline, the value has to be reconstructed from whatever evidence exists, and that is a weak position.

There is also an anti-degradation rule. Where on-site habitat has been degraded on or after 30 January 2020 and the degradation was not authorised, the pre-development value is assessed as at the date immediately before the degradation occurred. Clearing scrub to tidy a site before applying therefore raises the baseline instead of lowering it. Keep dated aerial imagery and photographs for any site bought after that date, because the burden of showing the earlier condition falls on the applicant.

The habitat survey underpinning the baseline must be carried out to the UK Habitat Classification and in a condition-assessable season. A winter survey of grassland will not support a defensible condition score, and a preliminary ecological appraisal commissioned at the right time of year is the best value insurance available on a development site.

Habitat losses and the completed metric

The plan must show what is lost, what is retained and what is created or improved, with the statutory biodiversity metric calculation attached in full rather than summarised.

Authorities check the metric file itself, not the headline percentage. The usual points of challenge are:

• condition assessments that have been scored generously, particularly for modified grassland and hedgerows
• habitat parcels mapped at the wrong area, where the drawing and the metric disagree
• retained habitat counted as retained when the construction layout clearly affects it
• missing or optimistic time-to-target-condition entries, which drive the temporal risk multiplier
• strategic significance scored as high without pointing to the local nature recovery strategy or plan policy that says so

The trading rules sit behind all of this. Habitat of medium, high or very high distinctiveness has to be replaced with habitat of the same type or better, so a scheme that loses a species-rich hedgerow cannot make it up with amenity grassland however large the area. The overlap between hedgerow units in the metric and the separate protections in the Hedgerows Regulations catches people out, and the detail of hedgerow units and the Hedgerows Regulations overlap repays attention before a layout is fixed.

The metric must be completed by a competent person. The Environment Act regime expects that, and a draft produced from structured data is a starting point for the ecologist, never a replacement for one.

On-site, off-site and credit components

The 10 per cent gain can be met from three sources, and the plan must set out which is doing what.

The hierarchy is not merely a preference. On-site measures come first, off-site units next, and credits last, and an authority can refuse a plan that reaches for credits without showing why on-site and off-site options were unavailable.

Significant on-site enhancement has to be secured for at least 30 years, which means a habitat management and monitoring plan with named responsibilities, a monitoring schedule and a funding route. A one-page landscape maintenance note will not satisfy it. Where the land will be sold on, say who holds the obligation after sale.

Irreplaceable habitat and the separate statement

Ancient woodland, ancient and veteran trees, blanket bog, limestone pavement, coastal sand dunes, spartina saltmarsh swards and lowland fen are treated as irreplaceable habitat. The metric cannot express their loss, so the percentage approach does not apply to them.

Where development affects irreplaceable habitat, the plan must include a statement setting out the arrangements made for compensating for the loss, and the authority cannot approve the plan unless it is satisfied with those arrangements. In practice this is a high bar, and the Framework's own protection for irreplaceable habitats means most schemes should be redesigned to avoid the habitat rather than proposing to compensate for it.

Identify irreplaceable habitat at the appraisal stage. Finding an ancient hedgerow or a veteran tree after the layout is fixed is one of the more expensive discoveries in development.

Who submits the plan and who approves it

The developer submits the plan to the local planning authority that granted permission. The authority approves or refuses it, and the 2024 regulations provide an appeal route where approval is refused or the plan is not determined, running broadly as other post-permission appeals do. Check the current deadline in the regulations, because it is shorter than the general appeal period.

Phased schemes work differently. An overall plan covering the whole site is submitted alongside phase plans for each phase, so the first phase cannot be allowed to take the easy gains and leave the later phases short.

The authority is checking compliance with Schedule 7A, not exercising planning judgement afresh. An approved plan does not bless the development. It confirms that the gain obligation has been properly calculated and secured, which is why an authority can refuse a plan for a scheme it has already permitted.

Why plans get rejected

The commonest reasons are administrative rather than ecological.

1. The baseline date is not stated, or the stated date does not match the application date.
2. The metric file is not supplied, only a summary table or a percentage.
3. Condition scores are not evidenced by a survey report or the survey was done out of season.
4. On-site habitat works are shown in the metric but not secured by any condition or obligation.
5. Off-site units are described but not allocated on the register, so they cannot be verified.
6. The habitat management and monitoring plan has no funding route or no named party for the 30-year period.
7. Drawings and metric areas disagree, often by enough to flip the result.

Work backwards from that list when assembling the submission. A plan that states its baseline date clearly, attaches the metric, cross-references each habitat measure to a condition number and names the party responsible for management tends to be approved first time.

Reviewing the ecology evidence before it goes in is worth the time, and the practical approach to reviewing another consultant's ecology report applies equally to a gain plan prepared by a third party. A biodiversity net gain assessment draft gives you the structure and the policy framing, and a competent person completes and signs off the metric.

See which ecology and gain documents a site is likely to need by browsing the report categories and starting a draft.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.