Biodiversity net gain on a section 73 application
A section 73 permission is a new permission, so the biodiversity gain condition has to be considered again. Which variations are exempt, when the metric must be rerun and how to sequence the work.
A section 73 permission is a new planning permission, so the biodiversity gain condition has to be considered afresh every time you vary a scheme. Whether it bites depends on the original permission rather than on the variation, and the exemptions written into the regime mean that most variations of older consents stay outside it.
Get this wrong in either direction and the consequences are expensive. Assume the condition applies when it does not and you have commissioned a metric for nothing. Assume it does not when it does and you have a permission that cannot lawfully be implemented until a gain plan is approved.
How the deemed condition attaches on a variation
Under the Environment Act 2021 regime, most planning permissions granted in England carry a deemed condition that development may not begin until a biodiversity gain plan has been submitted to and approved by the local planning authority.
The condition is deemed rather than drafted, so it does not appear on the decision notice in the way an ordinary condition does. That catches people out on section 73 decisions, where the decision notice lists the conditions being varied and carried forward, and the biodiversity gain condition sits behind all of them by operation of the statute.
The regime began on 12 February 2024 for major development and 2 April 2024 for small sites. Different arrangements apply to nationally significant infrastructure, and the current position on those should be checked rather than assumed.
Permissions granted before the regime began
The exemptions carry the weight here. A section 73 permission is generally exempt where the permission it varies was granted before the regime applied, or was granted on an application made before the relevant date.
That is a sensible rule and a broad one. A 2019 outline consent varied in 2026 does not acquire a biodiversity gain condition by virtue of the variation, and neither does a 2023 full permission granted on an application made in 2022.
What it does not do is freeze the scheme forever. The exemption attaches to the original permission and its variations, and a fresh application for a materially different scheme is a new permission subject to the condition in the ordinary way.
Check the application date as well as the grant date, and keep the evidence of both in the file. Where a permission has been varied several times, the chain runs back to the original, and the registration reference for that original consent is what the authority's ecologist will ask for.
When a variation brings a scheme into the regime
Two situations pull a previously exempt scheme in.
The first is where the variation is so extensive that it is not properly a section 73 at all. A section 73 cannot change the description of the development, and an authority faced with a variation that does so should refuse it and ask for a fresh application. That fresh application is a new permission and the condition applies.
The second is where the original permission was already subject to the condition. Then the section 73 permission carries its own condition, and the question becomes whether the approved plan still describes what is being built.
The Levelling-up and Regeneration Act 2023 also created a new route for varying permissions alongside section 73, and the position on when that route is available should be checked at the time, because it affects which permission is the operative one.
Revising a gain plan that is already approved
Where the original permission carried the condition and a plan was approved, a variation that leaves the habitat position untouched does not need the whole exercise repeating. A change to the internal layout of a building, to materials, or to a phasing trigger, generally does not alter a single figure in the metric.
Where the variation changes the site layout, the extent of retained habitat, the position of a sustainable drainage feature or the boundary of the works, the metric has to be rerun and a revised plan submitted for approval.
The practical test is whether any input to the metric changes: habitat parcels, areas, distinctiveness, condition, strategic significance, the temporal risk from a longer delivery programme, or the difficulty of creation. A revised plan that shows the same headline percentage by a different route still needs approving, because the authority approves the plan rather than the percentage.
A Biodiversity Net Gain Assessment has to be prepared by a competent person under the Environment Act 2021 regime, and an AI-drafted document is the starting point for that person rather than a replacement.
Baseline questions on a site that is part built
This is where variations get difficult. The pre-development biodiversity value is assessed as at the relevant date for the original permission, not as at the date of the variation. A site that was pasture in 2024 and is a construction compound in 2026 is still assessed against the pasture.
Sites cleared or degraded after 30 January 2020 are also caught by the anti-degradation provision, so habitat removed in anticipation of development is valued as it was immediately before the removal. Clearing a site to improve the numbers does not work, and the authority's ecologist will ask for historic aerial imagery.
Where the original baseline survey is old, the authority may accept it for the varied scheme because the relevant date has not moved. Where the survey was thin, expect to be asked for more. A Preliminary Ecological Appraisal done properly at the outset is what makes a variation three years later straightforward.
Evidence the baseline with the original survey report, the original metric file and a note explaining the relationship between them. Do not rebuild the baseline from a current survey of a construction site.
Evidence to submit with the variation
For an exempt variation, the submission is short: a statement identifying the original permission by reference and date, the application date for that permission, and the exemption relied on. Put it in the Planning Statement rather than in a covering email, because the file needs to show the reasoning.
For a variation inside the regime, expect to provide the updated metric file in its native format, a revised biodiversity gain plan, an updated habitat management and monitoring plan where the on-site delivery has changed, and evidence of any off-site units or credits.
Where off-site units are involved, the allocation to the permission is recorded on the biodiversity gain sites register, and a change to the scheme can mean changing that allocation. That is a separate administrative step with its own timing, and it is the one most often left until last.
Sequencing the variation and the plan
Work backwards from the date you need to be on site.
- Establish whether the original permission is exempt, using the application date and the grant date.
- If it is not exempt, identify whether any metric input changes under the varied scheme.
- Rerun the metric and revise the plan before the section 73 application is submitted, so the two can be considered together.
- Submit the gain plan for approval after the section 73 permission is granted, because the plan is approved against a permission that exists.
- Allow eight weeks for that approval, and longer where off-site allocation has to change.
The mistake to avoid is treating the gain plan as a discharge item to deal with during mobilisation. It is a barrier to starting work, the authority has no duty to approve it quickly, and a scheme sitting on a funded start date with an unapproved plan has no lawful way forward.
One honest uncertainty: authorities differ on how much change to a varied scheme triggers a full re-run rather than a short note, and there is little published guidance on where that line sits. Ask the authority's ecologist before submitting, and record the answer.
Browse the report types and start a draft, then send it for professional review.
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
Does a section 73 variation trigger biodiversity net gain?
Only where the permission being varied was itself subject to the regime. A section 73 permission is generally exempt where the original permission was granted before the regime applied, or was granted on an application made before the relevant date. Check the application date as well as the grant date and keep evidence of both.
When did the regime start?
12 February 2024 for major development and 2 April 2024 for small sites in England. Different arrangements apply to nationally significant infrastructure, so check the current position for those. The dates matter because the exemption for section 73 permissions works by reference to the original permission rather than the variation.
Does an approved gain plan carry over to the varied scheme?
Where the variation changes nothing that feeds the metric, such as internal layout or materials, the approved plan can stand. Where the site layout, retained habitat, drainage features or works boundary change, the metric has to be rerun and a revised plan approved. The authority approves the plan, not the headline percentage.
How is the baseline assessed on a part built site?
Against the relevant date for the original permission, not the date of the variation. A field that was pasture when the original application was made is assessed as pasture even if it is now a compound. Habitat cleared after 30 January 2020 is valued as it was immediately before clearance, and aerial imagery is used to check.
When should the gain plan be submitted?
After the section 73 permission is granted, because the plan is approved against a permission that exists. Prepare the revised metric before the section 73 application so both can be considered together, then allow around eight weeks for approval, and longer where an off-site unit allocation has to be changed on the register.
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.