What competent person means for biodiversity net gain

Nobody licenses biodiversity net gain assessors. There is no register, no certificate and no statutory competence test, which sits oddly beside a regime that expects a competent person to complete the statutory metric and makes the result a condition on almost every planning permission. Competence here is a matter of evidence rather than paperwork, and the evidence a local planning authority looks for is fairly consistent.

Understanding what that evidence is will save you a delayed start on site. The metric is checked after permission, when the programme is least forgiving.

Where the expectation of competence comes from

The Environment Act 2021 inserted the biodiversity gain condition into the Town and Country Planning Act 1990. Mandatory net gain applied to major development from 12 February 2024 and to small sites from 2 April 2024. The scheme requires a ten per cent uplift in biodiversity value, measured with the statutory metric published by Defra, secured and maintained for at least 30 years.

The statute itself does not define a competent person. The expectation comes from the metric's user guide and from the way authorities apply it: the metric is a calculation tool that turns field observations into units, and the tool is only as good as the observations fed into it. Defra's guidance is explicit that the metric should be applied by someone with the relevant ecological skills.

So the question a council asks is not "does this person hold a certificate", but "could this person defend the habitat classification at appeal".

Habitat classification and condition assessment

Two judgements drive everything downstream.

The first is classification. Habitats are recorded using the UK Habitat Classification, which distinguishes, for example, modified grassland from other neutral grassland, and lowland mixed deciduous woodland from a line of trees. Get that wrong and the distinctiveness band changes, which changes the number of units before any condition scoring happens.

The second is condition. Each habitat type has published criteria, and the assessor scores the parcel as good, moderate or poor against them. This is where the largest arguments occur, because the difference between moderate and good on a hectare of grassland can be worth more units than the whole of a small scheme's proposed planting.

Both judgements are made standing in the field, in the growing season, with a plant identification skill set. Neither can be made from aerial imagery, and a metric produced without a site visit is the first thing a council ecologist looks for.

Who signs the metric and what that means

The metric file records the assessor's name and the survey date. That is the signature, and it carries three practical consequences.

It exposes the surveyor to professional scrutiny, which is the point. It ties the baseline to a date, and councils generally expect the survey to be recent, with older data challenged in the same way as protected species survey data. And it creates a chain of responsibility that matters when the biodiversity gain plan is submitted months or years later by a different party.

Keep the native metric file as well as the printed summary. Councils ask for the calculation tool itself so they can see the habitat parcels, the areas and the condition scores as entered, and a scheme that supplies only a PDF extract of the results will usually be asked for the file anyway.

Where the assessor is a member of a professional body, that membership carries a code of conduct and a complaints route. It also usually carries professional indemnity insurance, which is worth confirming rather than assuming, particularly on a scheme where an error would mean buying off-site units.

How councils check the assessor

Authorities vary in how much ecological capacity they hold. Some employ an in-house ecologist, some buy in a county ecology service, and some rely on the applicant's own consultant with a light review. The checks that recur are these:

• Is there a named surveyor with stated qualifications, and a survey date inside the growing season?
• Does the habitat plan match the site layout drawing parcel for parcel, with areas that add up to the red line?
• Are condition scores justified against the published criteria, with the criteria assessment shown rather than asserted?
• Have the trading rules been respected, so that losses of medium or high distinctiveness habitat are replaced with the same or better?
• Are irreplaceable habitats, such as ancient woodland, correctly excluded from the metric and dealt with in policy terms instead?

A preliminary ecological appraisal that describes the site in words the metric contradicts is a reliable way to attract all five questions at once.

Consequences of a metric completed badly

The timing is what hurts. Planning permission can be granted with a poor metric, because the gain plan is a post-permission document. The reckoning arrives when the plan is submitted, the authority declines to approve it, and the site cannot lawfully start.

Illustrative example: a 40-unit scheme records a paddock as modified grassland in poor condition and proposes wildflower meadow to compensate. The council's ecologist visits, finds a species-rich sward, and reclassifies it as other neutral grassland in moderate condition. The baseline units rise, the proposed on-site planting no longer clears ten per cent, and the developer has to buy off-site units in the same national character area at short notice. The delay, not the survey fee, is the expensive part.

There is a second failure mode. Where on-site habitat is proposed that the layout cannot actually accommodate, the metric passes and the landscape scheme does not, and the mismatch surfaces at discharge of conditions. Root protection areas, adoptable highway margins, sub-station plots and attenuation basins all eat into the space a landscape drawing shows as new habitat, and the person entering the metric rarely sees the drainage layout unless someone sends it to them.

Briefing an assessor before the survey

Give them the red line boundary, the existing topographical survey, the draft layout and the landscape strategy, and give them all four before they visit. An assessor who arrives without knowing which parcels will be retained cannot advise on where value is being lost cheaply.

Ask for three things in the fee proposal:

1. A stated survey window and a named surveyor with their qualifications and experience.
2. A condition assessment recorded criterion by criterion, with the reasoning shown rather than a bare score.
3. An indicative metric run at layout stage, before the drawings are fixed, so the design can respond.

That third point is where most of the money is saved. Retaining a hedgerow, widening a buffer or keeping a single mature tree is nearly free at sketch stage and impossible after the drainage layout is set.

The biodiversity net gain assessment that accompanies the application should tell the same story as the metric file and the landscape drawing. Where you want a specialist to review a draft before it goes in, PlanScope's professional directory is the route to a reviewer who can check and sign off the document.

The Environment Act 2021 regime expects the statutory metric to be completed by a competent person and the biodiversity gain plan to be approved by the local planning authority, so treat a PlanScope draft as a starting point for that professional rather than a substitute for them. For specialist technical reports, qualified professional input may be required. 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.