Section 73 applications and the biodiversity gain plan

Whether a section 73 biodiversity gain plan is needed depends on two things: when the original permission was granted, and whether the amendment changes the habitat position. A section 73 permission is a new planning permission, so the deemed biodiversity gain condition attaches to it in principle. But the regulations made under the Environment Act 2021 carry a transitional exemption for variations of permissions that predate the regime, and for amendments that leave the biodiversity position untouched the practical answer is usually a plan that reproduces the approved one rather than a fresh exercise.

Get that distinction wrong in either direction and you either stall the scheme or build out without a lawful plan.

Whether a variation reopens the gain plan

Start with the date of the original permission. The mandatory regime applied to major development from 12 February 2024 and to small sites from 2 April 2024, and the regulations exempt a section 73 permission where the original permission was granted, or applied for, before the relevant date. So a variation of a 2022 permission does not drag a pre-regime scheme into biodiversity net gain, which is a relief for long-running consents and a surprise to applicants who assumed the opposite.

Where the original permission was itself subject to the gain condition, the position is different. The condition attaches to the new permission, so a plan has to be in place for it before development proceeds under that permission.

What the regulations avoid is re-baselining. The pre-development biodiversity value is taken from the original permission rather than reassessed at the date of the variation, which means habitat lost during the build does not change the arithmetic and a partly built site is not penalised for its current condition.

Changes that alter the habitat baseline

The amendments that need a revised plan are the ones that change what is lost or what is created. In rough order of likelihood:

• A change to the red line or the developable area that takes in land not previously assessed
• A layout change that removes a retained habitat parcel, a tree group or a length of hedgerow
• A change to the landscape proposals that reduces the area or the target condition of created habitat
• A change of surfacing or levels across a parcel earmarked for enhancement
• A change to the phasing that moves habitat delivery into a later phase

Any of these alters the metric output, so the ecologist has to rerun the calculation and the revised plan has to show the new figures against the original baseline. Where the revision produces a shortfall, it has to be made up, by on-site redesign, by registered off-site units or by statutory credits.

The one to watch is the apparently trivial change. Moving a bin store onto a grass verge that was counted as created habitat is a small drawing change and a real unit change.

Changes that only affect delivery

Plenty of section 73 applications touch nothing ecological. A change to window positions, materials, internal layout, unit mix, an extension of the time limit for submission of details, or the wording of an unrelated condition leaves the habitat baseline and the habitat proposals exactly where they were.

In that situation the sensible course is to apply for the variation, state in the covering letter that the biodiversity position is unchanged, attach the approved plan and the metric output that supports it, and ask the authority to approve it as the plan for the new permission. Most authorities handle it that way, because the alternative is to re-approve identical figures.

Say it explicitly though. A section 73 application that is silent on biodiversity invites a holding objection from the ecology officer and a request for information that takes a fortnight to answer.

Approving a revised plan

A revised plan goes through the same route as the original: it is submitted to the local planning authority and has to be approved before development proceeds under the new permission. The content is the same as any gain plan, with the addition of a reconciliation.

That reconciliation is the useful part of the document. Set it out as a short table showing, for each habitat parcel, the original position, the revised position and the difference, with the totals at the bottom and the percentage against the original baseline. An officer who can see the delta in one page will approve it far faster than one who has to compare two metric outputs.

Where the gain was secured by a section 106 agreement, check whether that agreement needs a deed of variation to match. An approved plan that no longer corresponds to the obligations in the agreement is a problem that surfaces at the point of sale or discharge, not at approval. A Biodiversity Net Gain Assessment prepared for the variation should cross-refer to the agreement by clause.

Where a fresh application is needed instead

Section 73 has limits that have nothing to do with ecology, and they bite here. The power varies conditions, so it cannot be used to change the description of development, and the courts have held that a variation cannot produce a permission whose conditions conflict with its own description. A scheme whose unit numbers or footprint change beyond what the description allows needs a new full application.

A full application resets the baseline to the date of that application, which is where the ecological consequence appears. On a site where habitat has been cleared during construction, that reset can work either way, so model both routes before choosing. The Levelling-up and Regeneration Act 2023 added a separate variation power for minor changes, and both its scope and the date it took effect should be checked against the current legislation before you rely on it.

Evidence for the variation

For an amendment with ecological consequences, submit the revised metric output with the calculation file, a plan comparing the consented and proposed habitat layouts at the same scale, the revised habitat management and monitoring proposals, and the reconciliation table. Where retained habitat has deteriorated since the original survey, say so and explain how the baseline is still the one from the original permission.

Where the scheme involves retained trees or hedges, the arboricultural information has to match the ecology. A revised layout that moves a building within a root protection area produces an arboricultural objection and an ecology objection at the same time, and a Preliminary Ecological Appraisal and tree survey that disagree with each other will be challenged. Our notes on reviewing another consultant's ecology report and on connectivity conditions such as hedgehog gaps cover the detail that tends to be lost on amendment.

Avoiding a unit shortfall on amendment

Three habits prevent most of these problems. Treat the habitat layout as a fixed constraint in the same way as the drainage strategy, so that it appears on the engineering drawings rather than only on the landscape plan. Ask the ecologist to sign off any layout change before it is submitted, which costs an hour and saves a resubmission. And keep headroom above the required minimum on the original plan, because a scheme sitting exactly on the threshold has no tolerance for the inevitable drawing changes.

The honest uncertainty here is how authorities will treat accumulated minor variations over a long build out. Each one looks immaterial. Together they can erode the gain, and nobody is yet auditing them systematically. Keep your own running total.

The statutory metric has to be completed by a competent person and the plan is approved by the authority, so an AI-assisted draft can assemble the reconciliation, the policy framework and the document structure, but the ecological judgements and the calculation stay with the ecologist. Browse the report types to see how the ecology documents fit together across an amended permission.

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.