The biodiversity gain plan and what the council approves
The metric is a spreadsheet. The gain plan is the submission the council actually approves, and no development may lawfully begin until it has been.
The biodiversity gain plan is the document your council approves before you may start work, and it is separate from the metric calculation everyone talks about. Most planning permissions in England now carry a deemed pre-commencement condition under Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021, which prevents development beginning until a biodiversity gain plan has been submitted to and approved by the planning authority.
The metric is a spreadsheet. The gain plan is the submission that explains what the spreadsheet shows, how you got there and who will look after the habitat for the next 30 years.
When the gain condition applies to your permission
The condition is deemed into planning permissions in England, so it appears on the decision notice or applies by operation of law whether or not the officer mentions it. Mandatory net gain took effect for major development on 12 February 2024 and for small sites on 2 April 2024.
Several categories sit outside the regime. Householder development is exempt. Self-build and custom build schemes are exempt within the stated limits on the number of dwellings and the site area. There is a de minimis exemption for development that affects only a very small area of on-site habitat and a very short length of linear habitat. Biodiversity gain sites themselves are exempt, as are some urgent Crown developments.
Do not assume an exemption. The self-build exemption in particular has conditions attached to it that a purchaser's solicitor will check, and a scheme that drifts above the limits during design loses it. Confirm the position in writing with the case officer at application stage, and record the reasoning in the application documents.
Where the condition does apply, it bites at commencement. There is no ability to start on the groundworks while the plan is being determined.
What the gain plan has to contain
The statutory content list is short and each item does specific work.
- Information about the steps taken or to be taken to avoid or minimise adverse effects on the on-site habitat, which is the mitigation hierarchy expressed as a narrative.
- The pre-development biodiversity value of the on-site habitat, with the date at which it was assessed.
- The post-development biodiversity value of the on-site habitat.
- Any registered off-site biodiversity gain allocated to the development.
- Any statutory biodiversity credits purchased.
- The completed statutory metric calculation and such other matters as the regulations require.
The item most often done badly is the first. A gain plan that jumps straight to the numbers, without explaining why the hedgerow could not be retained or why the layout puts the access through the best habitat parcel, invites the ecology consultee to ask for a revision. Answer the avoid and minimise questions before you present the arithmetic.
Keep the plan aligned with the Biodiversity Net Gain Assessment and with the landscaping drawings. Three documents describing three slightly different habitat layouts is the most common reason a plan goes back.
Evidencing the pre-development baseline
The baseline sets the target, so the council scrutinises it harder than anything else. It is assessed on the date of the application, or on an earlier date where that has been agreed, and it must be supported by a habitat survey carried out by someone competent to classify habitats under the relevant classification system.
There is an anti-degradation rule. Where on-site habitat has been degraded since 30 January 2020, the pre-development value is taken as the value immediately before the degradation, not the value of the cleared site. Councils ask for historic aerial imagery to check this, and a site cleared shortly before purchase is a problem the applicant inherits.
Two practical points for small sites. A Preliminary Ecological Appraisal carried out in winter may not classify grassland reliably, and condition assessment depends on the sward, so a survey in the growing season produces a defensible baseline. And where protected species are present, the licensing work runs on its own timetable, which a Protected Species Survey will set out.
On-site, off-site and credits in the plan
The gain has to be delivered somewhere, and the plan has to say where with enough precision for the authority to secure it.
On-site delivery is set out in the habitat management and monitoring plan, secured by condition or obligation for 30 years. Off-site delivery requires the gain site to be entered on the biodiversity gain sites register and the units to be allocated to your development before the plan is approved. Statutory credits sold by the government are the last resort in the hierarchy, and they are deliberately priced to be unattractive.
Sequencing matters here. Registration of an off-site gain site takes time and needs a legal agreement in place, so a scheme relying on off-site units should begin that process during the application rather than after permission.
Where the plan relies on a mixture, show the split clearly. Twenty per cent from on-site habitat creation, seventy per cent from a named registered off-site allocation, ten per cent from credits, with the metric outputs for each. Officers reject plans that present a total without showing how it is composed.
How the authority determines the plan
Submission is to the local planning authority that granted the permission, and the regulations set a period within which it must decide. Check the current period rather than assuming, because the biodiversity gain regulations have been amended since the regime started.
The decision is a straightforward approve or refuse. There is no partial approval, no ability for the authority to approve a plan subject to modifications you have not made, and no deemed approval by silence. If the authority does not respond, chase it rather than starting work.
Where a plan is refused, the reasons tell you what to fix and a revised plan can be submitted. There is also a route to challenge a refusal, handled through the appeals system, so read the decision carefully and take a view on whether the objection is to your evidence or to your interpretation of the rules.
What happens if the plan is rejected
Nothing can begin. The condition is a true pre-commencement condition, and starting development without an approved plan is a breach of condition which the authority can enforce, with no lawful implementation of the permission.
That has a second consequence people miss. If the permission is close to its expiry date and the plan is not approved, you cannot make a lawful start, and the permission can lapse. Build the gain plan timetable into the programme from the day permission is granted rather than treating it as a discharge of conditions item to be dealt with alongside materials samples.
Keeping the plan consistent with the approved drawings
The habitat parcels in the metric must correspond to the areas shown on the approved layout, the planting plan and the drainage drawings. Conflicts arise because these are drawn by different people at different times.
Run three checks before submission. Does every habitat parcel in the metric exist on the planting drawing at the same area? Does any attenuation basin, adoptable highway verge or service easement overlap a parcel counted as habitat creation? And does the management plan name someone responsible, with a funding mechanism, for the full 30 years?
Where changes are made later under section 73 or a non-material amendment, the plan may need revisiting, because a layout change that alters habitat areas changes the metric output. Ecology work and licensing, including any Bat Survey requirements, should be re-checked at the same time.
The statutory metric is expected to be completed by a competent person and the gain plan approved by the local planning authority. A licensed or competent professional is required here, and an AI-assisted draft is a starting point for that professional rather than a substitute.
Enter your postcode on PlanScope to see which ecology documents your site is likely to need.
This is general guidance rather than 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
Is the biodiversity gain condition on my decision notice?
It applies to most planning permissions in England whether or not the officer mentions it, because Schedule 7A to the Town and Country Planning Act 1990 deems the condition into the permission. Mandatory net gain took effect for major development on 12 February 2024 and for small sites on 2 April 2024.
Does self-build development need a gain plan?
Self-build and custom build schemes are exempt within the stated limits on dwelling numbers and site area, and householder development is exempt outright. The conditions attached to the self-build exemption are checked by purchasers' solicitors, so confirm the position in writing with the case officer and record the reasoning in the application.
What is the anti-degradation rule?
Where on-site habitat has been degraded since 30 January 2020, the pre-development biodiversity value is taken as the value immediately before the degradation rather than the value of the cleared site. Councils check this using historic aerial imagery, so a site cleared shortly before purchase creates a baseline problem the applicant inherits.
Can the council approve a gain plan with modifications?
No. The decision is approve or refuse. There is no partial approval, no power to approve subject to changes you have not made, and no deemed approval if the authority stays silent. Where a plan is refused, the reasons indicate what to fix, and a revised plan can be submitted.
What happens if I start work without an approved plan?
Nothing can lawfully begin. The gain condition is a true pre-commencement condition, so starting is a breach the authority can enforce and there is no lawful implementation of the permission. If the permission is near its expiry date and the plan is unapproved, you cannot make a lawful start and the permission can lapse.
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.