Who completes the biodiversity gain plan calculation

Nobody signs the biodiversity metric in the way an engineer signs a structural calculation. There is no statutory licence, no register of approved assessors and no signature block. What the biodiversity net gain regime does is place the burden on the developer to submit a biodiversity gain plan the local planning authority can approve, and the metric behind it has to have been completed by someone competent to do it.

That is a weaker-sounding requirement than a licence and a harder one to satisfy, because competence here means field skills. The person has to be able to classify habitats correctly and assess their condition against the metric's criteria, on site, in the right season.

What the gain plan contains and who submits it

Under the regime introduced by the Environment Act 2021, most planning permissions in England carry a deemed condition that development may not begin until the authority has approved a biodiversity gain plan. The applicant or developer submits it. The authority approves or refuses it.

The plan sets out the pre-development biodiversity value of the onsite habitat, the steps taken to minimise adverse effects, the post-development value of the onsite habitat, any registered offsite gains allocated to the development, and any statutory biodiversity credits purchased. The statutory metric supplies the numbers.

Requirements applied from 12 February 2024 for major development and from 2 April 2024 for small sites, with exemptions including a de minimis threshold for very small habitat impacts, householder applications and, relevant to many self-builders, an exemption for self-build and custom housebuilding within the stated size limits. Check whether you are exempt before commissioning anything, because the exemption is answered on the application form.

Competent person and what the regime expects

The metric user guidance and the government guidance both expect the metric to be completed by a competent person. The phrase carries a specific weight in planning legislation generally, discussed in the note on the meaning of competent person, and here it resolves into three things.

Habitat classification skill, meaning the ability to identify and record habitat types to the classification the metric uses. Condition assessment skill, meaning the ability to apply the metric's condition criteria to what is on the ground rather than to what the aerial photograph suggests. And familiarity with the metric itself, including the trading rules, the risk multipliers and the way the spreadsheet handles habitat creation and enhancement.

Ecological membership is the usual proxy. Membership of the professional institute for ecology and environmental management at an appropriate grade, with a competency statement covering habitat survey and condition assessment, is what most authorities look for. Chartered status helps. Neither is legally required, which is why the authority's scrutiny falls on the survey report rather than on the credentials.

Where an unqualified baseline creates a deficit

The baseline is the trap. An over-optimistic baseline, recording grassland in better condition than it is, makes the site harder to improve and can create a shortfall you then have to buy your way out of. An under-optimistic baseline is equally dangerous, because the authority's ecologist may reject it and substitute a higher figure at the approval stage, after the design is fixed.

Both failures come from desk-based assessment. A baseline derived from aerial imagery and a habitat layer, without a site visit at the right time of year, is the single most common reason a gain plan is refused.

Season matters. Grassland condition cannot be assessed sensibly in December, and a survey outside the optimal period should say so and explain what precautionary assumptions were applied. An extended season is sometimes defensible. A midwinter survey presented without caveat is not, and the note on whether a survey is still valid covers how long you can rely on one.

Trading rule errors a reviewer finds

The trading rules are where competent-looking metrics fail. The recurring errors:

• medium distinctiveness habitat lost and replaced with a different broad habitat type, which the rules do not permit
• high distinctiveness habitat treated as tradeable when it requires bespoke compensation
• irreplaceable habitat included in the metric at all, when it sits outside the metric and needs separate bespoke arrangements
• temporal risk multipliers omitted where habitat creation is programmed years after the loss
• difficulty multipliers ignored for habitats that are hard to create
• strategic significance claimed without a local nature recovery strategy or plan policy identifying the area
• offsite units allocated without evidence that they are registered and legally secured

Each of those produces a plan the authority must refuse rather than one it can negotiate. That is the practical difference between this and most planning documents: the gain plan is a compliance check rather than a matter of judgement.

The approval step and its timing

The gain plan is approved after permission is granted and before development begins. Two consequences follow for the programme.

First, the work cannot be left until then. The baseline survey has to happen before the application, because the design depends on what the metric says, and a layout drawn without it usually cannot achieve gain onsite.

Second, the approval itself takes time, and there is no appeal against a refusal of a gain plan in the way there is against refusal of permission. The remedy is to submit a better plan. Build that iteration into the programme rather than assuming approval.

Where onsite gain is impossible, offsite units or statutory credits fill the gap, and credits are deliberately priced as a last resort. Establishing the offsite route early costs far less than discovering you need it after the layout is fixed.

Briefing the survey so the plan is approvable

1. Commission the baseline survey in the optimal season, before the layout is drawn.
2. Ask for habitat parcels mapped with condition scores and the condition criteria evidence, rather than a single total.
3. Ask for the completed metric file as well as the summary figures, so the assumptions can be checked.
4. Ask the ecologist to state their competence for habitat classification and condition assessment in the report.
5. Get the habitat creation and improvement specification written as a management plan with target conditions and monitoring, because that is what the 30 year obligation secures.
6. Confirm early whether the scheme is exempt, and answer the question on the form deliberately.

A Biodiversity Net Gain Assessment is a report type where a competent person is legally expected under the Environment Act 2021 regime, and PlanScope's draft is a starting point for that professional rather than a substitute for them. The professional directory is the route for having a draft reviewed and signed off, and the 66 report types by category show which ecology documents usually travel together.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. For specialist technical reports, qualified professional input may be required.

Enter your postcode on PlanScope to see which reports your site is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.