Spatial risk multipliers in the biodiversity metric

The spatial risk multiplier reduces the value of off-site biodiversity units according to how far the gain site is from the development, in administrative and ecological terms rather than in kilometres. Units delivered in the same local planning authority area or the same National Character Area count in full. Units in a neighbouring authority or neighbouring character area are discounted. Units anywhere else in England are discounted further still.

It applies only to off-site delivery. On-site units are not touched by it, which is one reason a small on-site gain can outperform a much larger off-site one in the final arithmetic.

What the multiplier does to a unit count

The metric calculates post-intervention habitat units for the off-site parcel in the usual way, applying the distinctiveness, condition, strategic significance, difficulty and temporal risk steps. The spatial risk multiplier is then applied to that figure, reducing the units that count towards the development's 10 per cent obligation.

Its purpose is straightforward. Biodiversity lost in one place and replaced two counties away does not serve the same ecological network or the same people, so the metric prices that displacement. The discount is a deliberate incentive to deliver close to the impact.

Confirm the values against the version of the statutory metric actually in use on your scheme. The tool has been revised more than once, and a review that quotes a superseded figure is worse than one that quotes none.

The three tiers

Read the first row carefully, because the test is disjunctive. A gain site in a different local planning authority still attracts no reduction if it falls within the same National Character Area as the development. That saves a great many schemes near an administrative boundary, and it is the single detail most often missed in submitted metrics.

The second row works the same way. Either a neighbouring authority or a neighbouring character area is enough for 0.75.

A 0.5 multiplier means half the units delivered on the ground count towards the obligation. A developer buying units in a distant habitat bank is therefore buying roughly twice as many as the headline requirement suggests, which is a point worth making to a client before contracts are signed rather than after.

Determining the tier for a gain site

Three checks, in order.

First, establish the local planning authority area containing the development and the one containing the gain site, and whether those areas share a boundary. Two-tier areas need care: the relevant authority is the local planning authority, and unitary, district and National Park boundaries all need checking against the correct dataset rather than a general map.

Second, establish the National Character Area for each. Natural England defines these as areas of distinctive landscape character, and the boundaries follow landscape rather than administration, so they cut across authority lines freely. The boundaries are published as a spatial dataset and can be checked on MAGIC.

Third, apply the tier and record both the authority names and the character area numbers and names in the metric and the covering report. A reviewer should be able to verify the tier without repeating the exercise.

Statutory biodiversity credits sit outside this. They are purchased from the government as a last resort and are not treated as an off-site gain site for spatial risk purposes.

Strategic significance is a separate adjustment

Reviewers conflate these two, and they do different things at different points.

Strategic significance asks whether the location of the habitat is identified in a local strategy as important for nature recovery. The metric applies an uplift where it is: a high strategic significance multiplier where the area is formally identified in a local strategy for habitat creation or enhancement, a medium one where the location is ecologically desirable but not formally identified, and no uplift where neither applies. Confirm the numerical values in the metric version in use.

Local Nature Recovery Strategies are the source, as they are published by the responsible authorities. Where one is not yet in place for the area, the metric expects reliance on the local plan, biodiversity opportunity mapping or an equivalent adopted document, and the report should say which was used and why.

So a gain site can carry a strategic significance uplift and a spatial risk reduction at the same time. They are not alternatives and neither cancels the other.

An illustrative calculation

Take an off-site parcel that generates 20 post-intervention habitat units after distinctiveness, condition, difficulty and temporal risk have been applied.

If the parcel sits in the same National Character Area as the development, the spatial risk multiplier is 1.0 and 20 units count. If it sits in a neighbouring character area and a neighbouring authority, the multiplier is 0.75 and 15 units count. If it sits in a different region entirely, the multiplier is 0.5 and 10 units count.

Against a requirement of, say, 12 units, the first parcel delivers a surplus, the second delivers a modest one, and the third falls short by two units and sends the applicant back to the market. This example is illustrative and the actual numbers depend on every earlier step in the calculation.

Errors that inflate the delivered units

Six appear regularly in submitted metrics.

Testing the authority boundary only, and missing that the same National Character Area applies. This inflates or deflates the answer depending on which way the error runs, and it is the most common of the six.

Treating adjacent as neighbouring where the areas meet only at a point, or where an intervening area lies between them.

Using ceremonial county or district boundaries in place of local planning authority boundaries, which diverge in two-tier and National Park areas.

Applying spatial risk to on-site units. It does not apply on site, and a metric that shows a spatial multiplier against on-site parcels has been filled in wrongly.

Applying the multiplier before the difficulty and temporal risk steps, which changes the result.

Recording the character area by name from memory rather than from the dataset. Names are similar and adjacency is not always what it looks like on a small-scale map.

The wider set of problems councils find in submitted metrics is set out in the note on biodiversity metric errors, and several of them compound with this one.

Checking this step in a submitted metric

1. Open the off-site tab and read the location fields, not the summary sheet.
2. Confirm the local planning authority for the development and for each gain parcel, from the authoritative boundary dataset.
3. Confirm the National Character Area for each, and check adjacency against the published boundaries rather than an impression.
4. Check that the multiplier recorded matches the tier those two checks produce.
5. Confirm no spatial multiplier has been applied to on-site parcels.
6. Check the order of operations, so that spatial risk follows difficulty and temporal risk.
7. Cross-check the strategic significance entry against the relevant Local Nature Recovery Strategy or the document used in its place.

Where the numbers are close to the 10 per cent threshold, a single tier error is enough to turn a compliant gain plan into a non-compliant one, and the error usually surfaces after the section 106 agreement has been drafted. That is the point at which it becomes expensive.

Habitat delivery timing feeds into the same arithmetic through the temporal risk step, and the practicalities of that are covered in the note on habitat creation planting seasons and failure. Baseline survey quality underpins all of it, which is why a properly scoped Preliminary Ecological Appraisal matters more than any later adjustment.

Reviewers signing off a metric should check this step explicitly and say so in the review note. A Biodiversity Net Gain Assessment drafted by PlanScope is a starting point for that professional rather than a substitute for their judgement.

This is general guidance, not legal advice. The statutory biodiversity metric is expected to be completed by a competent person under the Environment Act 2021 regime, and the biodiversity gain plan must be approved by the local planning authority. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.