Council ecologists and who checks your BNG submission

The person who checks your biodiversity net gain submission is almost never the case officer. It is an ecologist: employed in house by the larger authorities, provided through a shared county ecology service in many two-tier areas, or bought in from a consultancy where the council has no capacity. They read the metric, not the covering letter, and they check the habitat condition assessments against what an ecologist would have recorded on that site.

That is worth knowing before you commission anything, because a metric completed from an aerial photograph is obvious to the person assessing it within about a minute.

Who gives councils ecological advice

Three models dominate.

Unitary authorities and larger boroughs usually employ one or more ecologists directly, sitting alongside the tree officer and the conservation officer as internal consultees. Two-tier districts often buy advice from a county-level ecology service, which may cover a dozen authorities and works to a service-level agreement with a response time. Smaller councils and some unitaries commission advice case by case from a framework consultant.

The model matters for two practical reasons. Response times differ, and a shared service under pressure will prioritise majors over small sites. And the advice you get at pre-application may come from a different person than the one who assesses the submission, so put anything agreed in writing.

Natural England is a statutory consultee on protected sites, protected species licensing and certain designations. It is not a general consultee on biodiversity net gain, and it will not check your metric.

The biodiversity gain condition and how approval works

Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021, deems a biodiversity gain condition to be attached to most planning permissions in England. The regime applied to major development from 12 February 2024 and to small sites from 2 April 2024.

The mechanism is a two-stage one, and people routinely misunderstand the second stage.

1. At application, most councils require a completed statutory biodiversity metric showing the pre-development baseline and the post-development value, plus a statement of whether the applicant believes the condition applies.
2. Permission is granted with the biodiversity gain condition deemed attached.
3. Before development begins, the applicant submits a biodiversity gain plan for the local planning authority to approve. Development cannot lawfully start until it is approved.

So the condition is discharged after permission, not before, and the approval of the gain plan is a separate decision with its own timescale. Programme it. A scheme that expects to start on site four weeks after a decision notice, with no gain plan submitted, will not.

The plan itself sets out the pre-development biodiversity value, the steps taken to minimise adverse effects, the on-site enhancements, any off-site gains and any statutory credits, and the completed metric.

What the council checks in the metric

The ecologist's review follows a predictable path, and knowing it removes most of the back and forth.

• Whether the baseline habitat survey was carried out at a suitable time of year and to a recognised methodology, with a survey date on the report.
• Whether habitat types have been correctly classified under the UK habitat classification, since a misclassified grassland changes the unit total substantially.
• Whether condition assessments were carried out against the published criteria rather than assumed to be moderate.
• Whether the baseline reflects the site as it was, not as it is after clearance. Degrading a site before survey is caught by the rules on the retrospective baseline date.
• Whether proposed habitat creation is deliverable, with the right soils, hydrology and management, and whether the difficulty multipliers have been applied honestly.
• Whether trees have been entered correctly, which is where a Tree Survey and Arboricultural Impact Assessment to BS 5837:2012 and the metric need to agree with each other.

The most common reason for rejection is not a shortfall in units. It is inconsistency between documents: an ecology report describing species-rich grassland, a metric recording it as modified grassland, and a landscape plan showing amenity turf.

Small sites and the pre-commencement condition

Small sites, broadly those below the major thresholds and meeting the criteria in the regulations, can use the small sites metric, which is shorter and needs less habitat condition data. It does not remove the requirement for a competent assessment.

Certain development is exempt from the biodiversity gain condition altogether, including householder development, development below the de minimis threshold where the site contains only a very small area of on-site habitat and no significant hedgerow, and self-build and custom build development meeting the conditions in the regulations. Check the current exemption wording rather than relying on a summary, because the detail has been amended.

For a self-builder, read the self-build exemption closely. It has conditions about the number of dwellings, the site area and the nature of the build, and claiming it wrongly means the gain condition still applies and development started without an approved plan is unlawful.

A Preliminary Ecological Appraisal is usually the document that supplies the habitat baseline, and councils expect a suitably qualified author. Professional review is strongly advised.

Where local policy asks for more than 10 per cent

The statutory minimum is a 10 per cent gain maintained for at least 30 years. Some adopted local plans and emerging plans require more, and the legal position is that a local policy can go beyond the national minimum where it is justified and viable.

Check three documents: the adopted local plan biodiversity policy, any biodiversity or green infrastructure supplementary planning document, and the council's validation list, which is where the requirement for a metric at application stage usually sits.

Where a gain cannot be delivered on site, the hierarchy is on-site first, then off-site, then statutory biodiversity credits as a last resort. Off-site units are secured through a section 106 agreement or a conservation covenant, and the agreement has to run for the full 30 years with monitoring and remedies. Our note on section 106 heads of terms for a small scheme covers how those clauses are structured.

Getting a competent person to sign the metric

This is the part that cannot be shortcut. The biodiversity net gain regime expects the statutory metric to be completed by a competent person, and the gain plan to be approved by the local planning authority. A Biodiversity Net Gain Assessment drafted in advance is a starting point for that professional, not a substitute for their survey, judgement or sign-off.

What competence looks like in practice: an ecologist with membership of a recognised professional body, experience of the habitat types on your site, familiarity with the current version of the statutory metric, and professional indemnity insurance. Ask which version of the metric they will use and when they can survey, because the optimal botanical survey window runs from April to September and a January baseline survey will be challenged.

Get the ecologist on board before the layout is fixed. Moving a hedgerow on a drawing costs nothing. Buying off-site units because the hedgerow was removed costs a great deal.

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, and for specialist technical reports qualified professional input may be required. This is general guidance rather than legal advice.