Competent person for the statutory biodiversity metric

The statutory biodiversity metric is not a form. It is the output of a habitat survey, and the figure it produces depends almost entirely on how the surveyor classified each parcel of habitat and what condition score they assigned. That is why the Environment Act 2021 regime expects a competent person to complete it, and why councils increasingly send metrics back rather than accept the number at face value.

There is no register of licensed metric assessors and no statutory qualification. Competence is demonstrated through evidence, and the developer carries the risk if it is absent.

What the Environment Act 2021 regime expects

Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021, imposes a biodiversity gain condition on most planning permissions in England. Development must deliver a biodiversity gain of at least 10 per cent measured by the statutory metric, and the gain must be maintained for at least 30 years.

The mechanism runs in two stages. At application, the applicant submits pre-development biodiversity value with the metric calculation and a statement of the habitats on site. After permission, a biodiversity gain plan must be submitted and approved by the local planning authority before development may lawfully begin.

The requirement applied to major development from 12 February 2024 and to small sites from 2 April 2024. Exemptions exist, including householder development, some self-build and custom build schemes, and development below the de minimis threshold for habitat loss. Check the current guidance rather than a summary, because the exemption list has been amended since introduction.

Defra's guidance and the metric user guide are explicit that the metric should be completed by a person with sufficient ecological competence. The local planning authority is entitled to test that.

Habitat classification and condition assessment skills

Two judgements drive the whole calculation.

The first is habitat classification under the UK Habitat Classification system. Getting a grassland into the right category, distinguishing modified grassland from other neutral grassland, or recognising that a scrappy field margin qualifies as a priority habitat, changes the distinctiveness score and therefore the units.

The second is condition assessment. Each habitat type has its own condition criteria, and the assessor has to apply them in the field against a defined set of attributes. A parcel scored good rather than moderate can move the pre-development baseline by a wide margin, and a baseline that is too high makes the 10 per cent gain harder to achieve.

The skills that underpin both are botanical identification to species level, familiarity with the current UK Habitat Classification definitions, the ability to apply condition criteria consistently, and enough field experience to know what a habitat looks like outside the optimal survey window.

Add competence in spatial risk categories, strategic significance and the connectivity elements, which are frequently mis-assigned.

Evidence a council checks in the gain plan

Councils have become considerably more forensic since 2024. The items an ecology officer looks at first are consistent.

1. The survey date and whether it falls within a defensible botanical survey window, generally April to September for grassland.
2. The habitat plan, and whether the mapped parcels match what aerial imagery and site photographs show.
3. Condition assessment sheets for each parcel, with the attribute-by-attribute scoring shown rather than a single conclusion.
4. Whether hedgerows and watercourses have been assessed on their own modules rather than folded into area habitats.
5. The trading rules, and whether losses of higher distinctiveness habitat have been compensated with habitat of the same or higher distinctiveness.
6. The 30-year management and monitoring proposals and how they will be secured.
7. Who completed the metric, their qualifications and their relevant experience.

Item seven is the one applicants forget. Put a short statement of the assessor's competence in the report: their qualifications, professional membership, years of relevant survey experience and a note of comparable work. It costs a paragraph and removes an easy line of challenge.

Where metric errors are usually found

Some errors recur so often they are worth listing.

Baseline inflation, where the pre-development condition is scored generously so the gain looks easier, then falls apart when the officer reads the condition sheets. Baseline deflation is the mirror error, usually accidental, and it exposes the applicant to a larger obligation than necessary.

Survey timing outside the botanical season, with condition assessed from a February walkover. Councils reject this routinely, and it is the single most common reason a metric is returned.

Missing hedgerow and watercourse modules on sites where those features are present. Both are assessed separately and both carry their own trading rules.

Habitat creation proposals that assume a condition at year 30 that the management plan will not deliver, and time-to-target multipliers applied optimistically. And off-site units recorded without the legal mechanism to secure them.

One honest observation: two competent ecologists surveying the same field on the same day can produce different condition scores. The metric is a structured judgement, not a measurement, and a report that shows its reasoning is far more defensible than one that shows only the total.

Site survey timing and competence

Habitat condition should be assessed when the vegetation can be identified, which for most grassland and open habitats means April to September. A survey outside that window is possible where the assessor sets out the limitations and, where necessary, applies a precautionary approach, but it should be flagged rather than hidden.

That timing sits alongside the other ecological seasons on a development programme. Where a site needs a preliminary ecological appraisal, commission it and the metric survey together so the same visit serves both, and so any protected species constraints surface early.

The metric assessor is not necessarily the same person as the licensed ecologist who deals with protected species. Survey licences for bats or great crested newts are a different competence entirely, and and a protected species survey must be carried out by a suitably licensed ecologist.

Briefing and reviewing a metric assessor

Brief for the output the council needs rather than for a number alone. Ask for the completed metric file, the habitat plan, per-parcel condition sheets, photographs, a statement of survey limitations, the trading rule check and the assessor competence statement.

When the report arrives, review it against three questions. Does the habitat plan match what you can see on aerial imagery? Are the condition scores supported by the attribute sheets rather than asserted? And does the post-development scenario rely on management the scheme will actually fund for 30 years?

A biodiversity net gain assessment drafted with structure and policy citations gives you a starting point and a checklist for that conversation. It does not replace the survey. The Environment Act 2021 regime expects a competent person to complete the statutory metric, and the biodiversity gain plan has to be approved by the local planning authority before development begins, so the professional input is the substance rather than a review of 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. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.