Biodiversity net gain disputes at appeal: what can be argued

Biodiversity net gain rarely appears on a refusal notice as a stand-alone reason, because the gain condition is discharged after permission rather than decided with it. A biodiversity net gain appeal therefore usually turns on something adjacent: the council says it cannot assess the proposal without ecological information, or it has refused to approve the biodiversity gain plan, or it has imposed conditions and obligations the applicant says go further than the statute allows. Knowing which of those three you are in decides what evidence you lodge.

The regime sits in Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021, and applied to major development in England from 12 February 2024 and to small sites from 2 April 2024.

Where the gain condition sits in the process

Most planning permissions in England are granted subject to a deemed condition that development may not begin until the local planning authority has approved a biodiversity gain plan. The plan sets out the pre-development baseline, the post-development value, the on-site and off-site habitat, and how the 10 per cent uplift is reached and held for at least 30 years.

The sequence matters for appeals. At the application stage, the authority is looking for enough information to be satisfied the uplift is achievable and that the layout does not foreclose it. Most local validation lists now require a completed statutory metric and a short biodiversity gain statement. At the gain plan stage, the authority is approving a document against the statutory tests, and refusal of that approval carries its own appeal route.

So a refusal for weak ecology is not a refusal on net gain. It is a refusal on the natural environment policies of the current National Planning Policy Framework and the duty in section 40 of the Natural Environment and Rural Communities Act 2006, and that distinction changes the shape of the statement of case.

Issues that can be argued

Appeals in this area cluster around a handful of arguments. Whether the authority had enough information to determine the application. Whether an exemption applies. Whether the metric has been run correctly. Whether off-site units are secured properly. Whether a condition or obligation meets the policy tests on necessity and reasonableness.

The weakest appeals are the ones that treat the metric output as self-evidently correct. An inspector will look at the inputs, and a baseline that nobody can verify on the ground is the usual soft spot. Our note on reading a refusal notice and turning it into a plan applies here more than most: the wording of the reason tells you which of the five arguments you are actually running.

Metric disputes and habitat classification

Most disagreement is about the baseline rather than the proposals. Habitat type is assigned under the UK Habitat Classification, and the gap between modified grassland and other neutral grassland, or between a line of trees and a native hedgerow, moves units in a way that can decide the outcome. Condition assessment is scored against published criteria, and two surveyors can read the same sward differently.

Three input questions come up repeatedly:

1. When was the baseline survey done, and was it in a season when the habitat could be identified at all? A February walkover cannot support a grassland condition score.
2. Has the site been degraded since 30 January 2020? Where habitat has been cleared or damaged after that date, the baseline is taken as the condition before the degradation, and the authority can require evidence of what was there.
3. Are strategic significance and spatial risk multipliers applied consistently, with the local nature recovery strategy or equivalent mapping cited?

A Preliminary Ecological Appraisal carried out by a suitably qualified ecologist is the evidence that answers all three, and at appeal it carries weight only if it describes method, dates and limitations honestly. Irreplaceable habitat sits outside the metric altogether. Ancient woodland, ancient and veteran trees, blanket bog and limestone pavement cannot be traded, and a scheme that affects them needs bespoke compensation and the policy test that goes with it.

Off-site units and their evidence

Where the uplift cannot be delivered on site, units are bought from a habitat bank or another landholding and have to be registered on the biodiversity gain sites register before the gain plan can be approved. Three things are tested at appeal: that the units exist and are allocated to your development, that the trading rules are satisfied, and that the 30-year management is secured by a planning obligation or a conservation covenant.

Statutory credits sold by the Secretary of State are the last resort, priced to be unattractive, and an appeal that relies on them should explain why on-site and market options were exhausted. Where the delivery route is an obligation, the drafting matters as much as the ecology, and a clause that ties management to a plan nobody has written yet will be probed.

Exemptions asserted and tested

Several exemptions exist, and asserting one is a common route into an appeal. Householder applications, self-build and custom housebuilding, development below the de minimis threshold of on-site habitat, biodiversity gain sites themselves and certain urgent Crown development all sit outside the regime. The de minimis test is narrow, measured in square metres of on-site habitat and metres of linear habitat, and a site with a scruffy verge can fail it.

Authorities test exemption claims with aerial imagery and their own records. If you are relying on an exemption, document the pre-existing surfacing with dated photographs and a measured plan, because the burden of showing the exemption applies sits with the applicant.

Conditions and obligations securing delivery

Even an uncontested gain plan comes with a habitat management and monitoring plan, monitoring reports at set intervals across the 30 years, and a mechanism for remedying shortfalls. Disputes arise where the authority wants a bond, a monitoring fee it cannot justify, or management obligations extending beyond the land in the application.

The tests are the familiar ones in national guidance on planning conditions and obligations: necessary, relevant to planning, relevant to the development, enforceable, precise and reasonable in all other respects. A condition requiring approval of a plan that the statute already requires is duplication, and inspectors have been willing to strike duplicated conditions out.

Preparing the evidence before lodging

Build the appeal file around the metric, not around the planning argument. That means the survey report with dates and method, the metric file in its native form rather than a printed summary, a plan showing habitat parcels against the layout, the register entry or allocation agreement for any off-site units, and a draft management plan.

Then be honest about the uncertainty. Inspectors respond better to an applicant who says the condition score is arguable and explains why the scheme works on either reading than to one who insists a judgement call was the only possible answer. Appeal decisions on net gain are indicative of how inspectors have approached the issue rather than binding precedent, so cite them for reasoning and not as authority. Third parties often raise habitat loss in their representations, and our guide to what objectors can do once an appeal starts explains the weight those carry. Withdrawing and resubmitting with a better baseline is sometimes the faster route, as our note on withdrawing an application before refusal sets out.

A Biodiversity Net Gain Assessment drafted in PlanScope gives you the structure and the policy references in minutes, and because the Environment Act 2021 regime expects the statutory metric to be completed by a competent person, that draft is the starting point for your ecologist rather than a replacement for one. Browse all 66 report types on PlanScope to see what else an appeal file usually needs.

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