A checklist for a biodiversity gain plan submission
The gain plan is submitted after permission and before work starts. Which exemptions apply to small and self-build sites, what evidence the plan needs and why plans get refused.
A biodiversity gain plan is submitted after planning permission is granted and before any work starts, and the local planning authority has to approve it. It is not part of the application, and treating it as a formality during mobilisation is how small schemes lose a summer.
For a self-builder or a small developer the first job is not writing the plan. It is checking whether an exemption applies, because several of them are aimed squarely at small sites and at self-build.
Checking the exemptions first
Work through these before commissioning anything.
- Is the application a householder application. Those are exempt.
- Does the development affect less than 25 m² of on-site habitat and less than 5 metres of linear habitat such as hedgerow. That is the de minimis exemption.
- Is the scheme self-build or custom build, of nine dwellings or fewer, on a site of no more than 0.5 hectares, where each dwelling is built or commissioned by the people who will live in it. That is the self-build and custom housebuilding exemption.
- Is the permission one that predates the regime, or granted on an application made before it applied.
- Is the site itself a registered biodiversity gain site.
The self-build exemption is narrower than people assume. It is not enough that the applicant intends to live in the house. The statutory definition of self-build and custom housebuilding has to be met, and the authority will ask how it is evidenced.
Where an exemption applies, say so in writing with the reasoning, and keep the evidence. Where none applies, the deemed condition is in force whether or not anybody mentioned it at committee.
When the plan is submitted and to whom
The plan goes to the local planning authority that granted permission, after the grant and before development begins. Allow eight weeks for determination and treat that as a minimum where off-site units are involved.
There is no route to start work while approval is pending. A condition that must be satisfied before work starts is a hard barrier, and work carried out in breach is unlawful and hard to regularise.
Where the permission is outline or the development is phased, the structure changes, with an overall plan and phase plans rather than a single document. That sits outside the scope of a straightforward small site submission.
Baseline evidence and the survey date
The pre-development biodiversity value comes from a habitat survey of the site, classified using the current habitat classification, with a condition assessment for each parcel.
Three things the authority's ecologist checks first. The survey date, because a survey taken outside the season for the habitats present is weak evidence. The parcel mapping, because the areas in the metric have to match the plan. And the condition scores, because condition moves units more than area does.
The baseline is fixed as at the relevant date for the permission rather than the date you submit the plan. Habitat cleared or degraded after 30 January 2020 is valued as it was immediately before the clearance, so tidying a site before survey does not help and does get noticed.
A Preliminary Ecological Appraisal carried out at the right time of year is what makes all of this straightforward later. Commissioning it after permission, in December, is what makes it slow.
What the metric outputs must show
Submit the completed statutory metric file itself, in its native format, not a summary table pasted into a report. Authorities need to open it and check the inputs.
The plan should set out the pre-development value in habitat units, hedgerow units and watercourse units as applicable, the post-development on-site value, the off-site allocation and any statutory credits, and the resulting percentage change against the baseline. The way those units are derived is explained in the piece on habitat units as the currency of net gain.
Show the trading rules are satisfied rather than asserting the headline figure. Losses of higher distinctiveness habitat cannot be made good with lower distinctiveness creation, and each module has to work in its own right.
Where irreplaceable habitat such as ancient woodland is present, the metric does not apply to it. That needs bespoke compensation agreed with the authority, and it is a reason to redesign rather than a line in a spreadsheet.
On-site, off-site and credits in combination
The hierarchy runs on-site first, then off-site units, then statutory credits as a last resort. Credits are deliberately priced to be unattractive.
For a small site, on-site delivery usually means hedgerow planting, a species-rich grassland margin, a small area of scrub or a pond, held out of the developable area. Draw those on a plan that matches the metric parcels and the landscape drawing, because three documents showing three different layouts is the most common reason a plan comes back.
Off-site units are bought from a registered biodiversity gain site and allocated to your permission on the register. That allocation is a separate administrative step with its own timing, and the plan needs the evidence of it. Arrange the purchase before submitting rather than after.
Small sites can use the small sites metric where the eligibility criteria are met, which reduces the survey burden. Check the criteria rather than assuming the site qualifies.
The 30 year management commitment
On-site habitat created or enhanced has to be maintained for at least 30 years, secured through a planning condition, a section 106 agreement or a conservation covenant.
That means a habitat management and monitoring plan setting out what is being created, the target condition, the management operations by year, the monitoring intervals, who is responsible and what happens if the target is not met.
For a self-builder this is the part that deserves thought. A 30-year commitment attaches to the land, passes to whoever owns it next, and shows up on a search. Design habitat that the eventual owner can actually maintain: a native hedge and a managed grassland margin are realistic, and a wet woodland needing specialist intervention is not.
The Landscape Strategy and the management plan should describe the same thing in the same units. Where they diverge, the authority follows the management plan.
Approval, refusal and resubmission
The authority approves or refuses the plan. Refusal usually comes down to one of a short list: the metric does not open or contains errors, the baseline survey is out of season or undated, the parcels do not match the drawings, the trading rules are not met, the off-site allocation is not evidenced, or the management plan lacks a responsible party.
Fix the reason and resubmit. There is also an appeal route where the refusal is wrong in principle, and the current procedure should be checked at the time rather than assumed, because the arrangements have been amended since the regime began.
A Biodiversity Net Gain Assessment must be prepared by a competent person under the Environment Act 2021 regime, and the authority approves the gain plan itself. An AI-drafted document gives that person a structured starting point, flags the site facts it does not hold, and does not replace the survey or the metric.
Before you submit, check you have: the metric file, the survey report with dates and condition sheets, a plan showing habitat parcels that matches the metric, the management and monitoring plan with a named responsible party, evidence of any off-site allocation, and a short statement tying the numbers to the permission reference.
Enter your postcode to see which reports a site is likely to need.
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. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
When is a biodiversity gain plan submitted?
After planning permission is granted and before development begins. It is not part of the application. Allow at least eight weeks for the authority to determine it, and longer where off-site units have to be allocated on the register. There is no route to start work while approval is pending.
Is a self-build house exempt from biodiversity net gain?
Only where the statutory test is met: nine dwellings or fewer, a site of no more than 0.5 hectares, and each dwelling built or commissioned by the people who will live in it. Intending to live in the house is not enough on its own, and the authority will ask how the self-build or custom build status is evidenced.
What is the de minimis exemption?
Development that affects less than 25 m² of on-site habitat and less than 5 metres of linear habitat such as hedgerow is exempt. It is measured against what the development affects, not the site area, so a small building placed on existing hard standing can qualify where a larger footprint on grassland does not.
Does the metric file itself have to be submitted?
Yes. Submit the completed statutory metric in its native format rather than a summary table, because the authority's ecologist needs to open it and check the inputs. The habitat parcels in the metric must match the areas shown on the submitted plan and on the landscape drawing.
How long does the management commitment last?
At least 30 years for habitat created or enhanced on site, secured by condition, section 106 agreement or conservation covenant. The habitat management and monitoring plan sets out the target condition, the operations by year, the monitoring intervals and who is responsible. The obligation runs with the land to future owners.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.