Off-site biodiversity units and the spatial risk multiplier
The statutory metric halves off-site units bought outside your local authority and National Character Area. Here is how the multiplier works, how registration sequences, and what to test in a habitat bank contract.
The spatial risk multiplier is the reason off-site biodiversity units cost more than the headline number suggests. Buy units in the same local planning authority area or National Character Area as your site and the metric counts them in full. Buy them in a neighbouring area and they are discounted to three quarters. Buy them further away and they are halved, so you need twice the habitat to deliver the same net gain. That discount, not the price per unit, is what usually decides where a scheme sources its off-site gain.
Developers often discover the multiplier after agreeing a price. By then the deal is sized wrongly.
Where off-site units sit in the hierarchy
Mandatory biodiversity net gain applies through the biodiversity gain condition in Schedule 7A to the Town and Country Planning Act 1990, inserted by the Environment Act 2021. It took effect for major development on 12 February 2024 and for small sites on 2 April 2024. The minimum is a 10 per cent gain, measured with the statutory biodiversity metric, maintained for at least 30 years.
National guidance sets an order of preference. On-site gains come first. Off-site gains, whether on land you control or units bought from a habitat bank, come second. Statutory biodiversity credits sold by government are a last resort, priced to make them unattractive.
The hierarchy is a planning consideration rather than an absolute bar, so an authority can accept off-site delivery where on-site provision is impractical. What it will want is an explanation of why the on-site figure is as low as it is, with the metric file showing what was tried.
How the spatial multiplier reduces unit value
Inside the statutory metric, off-site habitat creation and enhancement is multiplied by a spatial risk factor that reflects how far the compensation sits from the impact.
| Location of the off-site gain | Spatial risk multiplier |
|---|---|
| Within the same local planning authority area or the same National Character Area as the development | 1.0 |
| Within a neighbouring local planning authority area or neighbouring National Character Area | 0.75 |
| Outside both, and not neighbouring | 0.5 |
Check the figures against the version of the metric you are using, because the tool is periodically updated and the published user guide governs.
The arithmetic is unforgiving. A deficit of 2.4 biodiversity units met from a habitat bank two counties away needs 4.8 units of delivered habitat. At the same price per unit that doubles the cost, and it also doubles the land take, which matters where a bank has limited capacity in the habitat type you need.
Two other multipliers compound the effect. Strategic significance adds a modest uplift where the location is identified in a local strategy as a priority for habitat creation. Time-to-target delay reduces units where the habitat takes years to reach its target condition, and difficulty of creation reduces them again for habitats that are hard to establish. Woodland and species-rich grassland are the usual examples.
National Character Areas and strategy boundaries
Natural England divides England into 159 National Character Areas, which are landscape-scale units defined by geology, land use and settlement pattern rather than by administrative boundaries. For the multiplier, either a shared local planning authority area or a shared National Character Area is enough to score 1.0.
That gives more flexibility than people expect. A site on the edge of one district can often source units in an adjoining district that shares its National Character Area and still count them in full. Pull both boundaries onto one plan before you start negotiating, because the answer is frequently counter-intuitive.
Local Nature Recovery Strategies matter for strategic significance rather than for spatial risk. Where the strategy for the area identifies the off-site location as a priority for the habitat you are creating, the uplift applies. Where it does not, you are at the base rate, and no amount of ecological argument in the covering letter changes the multiplier the metric applies.
Finding and reserving units
The market is thinner than the headlines suggest, particularly for medium and high distinctiveness habitats. Trading rules require like-for-like replacement or better for anything above low distinctiveness, so a scheme losing species-rich grassland cannot discharge the deficit with amenity grassland however many units it buys.
Three questions decide whether a bank is usable.
- Is the gain site already registered, or only intended for registration? An unregistered site cannot have units allocated to a development.
- Is the habitat type in the register entry the one your metric file needs, at the distinctiveness you are losing?
- How many units remain unallocated, and is the allocation to you irrevocable once contracts are exchanged?
Reserve early on anything other than low distinctiveness grassland. Where the scheme removes hedgerow, note that hedgerow units are a separate module in the metric and sit alongside the older protection regime, a double track covered in our note on hedgerow units and the Hedgerows Regulations.
Registering off-site gain
Off-site gains must be entered on the biodiversity gain sites register maintained by Natural England before they can be allocated to a development. The register entry records the land, the habitat enhancement being delivered, the person responsible and the legal mechanism securing it for 30 years.
That mechanism is either a planning obligation under section 106 or a conservation covenant with a responsible body under the Environment Act 2021. Covenants suit land that is not connected to any planning application. Section 106 agreements suit land within the same authority's area, and the authority will usually prefer one because it is already a party.
The sequence that causes delay is this: the gain site operator applies to register, the application sits in a queue, and the biodiversity gain plan cannot be approved until the allocation exists. Because the biodiversity gain condition prevents development starting until the plan is approved, a registration delay stops the site. Ask for the register reference, not a promise of registration.
Pricing and contractual risk
There is no published national price for a biodiversity unit. Prices vary by habitat type, by region and by how much competition the bank faces, and a figure quoted in a trade article for one habitat in one county tells you nothing about yours. Get quotes.
What to interrogate in the contract matters more than the price.
- Whether the operator carries the risk of the habitat failing to reach target condition, or whether that risk returns to you.
- How the 30-year management is funded, and what happens if the operator becomes insolvent in year eight.
- Whether monitoring reports will be provided to you as well as to the authority, since the authority may hold you to the planning obligation.
- Whether the allocation can be withdrawn or reallocated, and on what notice.
- Whether the price is fixed on exchange or indexed to completion, which on a scheme with a long pre-commencement period is a real exposure.
One honest uncertainty: enforcement practice against gain site operators is still developing, and how authorities will respond to a bank that underperforms in year fifteen has not been widely tested. Treat long-term delivery risk as a commercial matter you price, not as something the regime has solved.
Evidence the authority needs before it approves the plan
A biodiversity gain plan relying on off-site units is refused or returned more often for missing paperwork than for ecological reasons. Submit the metric calculation file itself rather than a summary table, with the pre-development and post-development condition assessments and the habitat plans they were taken from.
Alongside it, the authority will expect the gain site register reference and the allocation evidence, the executed section 106 agreement or conservation covenant, a habitat management and monitoring plan covering the full 30 years, and the ecologist's statement explaining the multipliers applied. Where another consultant prepared the baseline, the points to test before you sign anything off are set out in reviewing another consultant's ecology report. On sites where habitat creation depends on soil handling, the method matters as much as the plan, and soil translocation on stripped ground is where that detail belongs.
A Biodiversity Net Gain Assessment draft from PlanScope will set out the structure, the policy context and the data the metric needs, and will flag where site facts are missing. 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 the draft is a starting point for that professional rather than a substitute, and a reviewer should sign it off before submission.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the spatial risk multiplier?
A factor in the statutory biodiversity metric that discounts off-site habitat according to its distance from the development. Gains inside the same local planning authority area or National Character Area count in full, gains in a neighbouring area count at three quarters, and gains outside both are halved. Confirm the values against the metric version you are using.
Can I buy units anywhere in England?
You can, but the economics usually rule it out. Units bought outside your local planning authority area and National Character Area are halved, so a deficit of 2.4 units needs 4.8 units of delivered habitat. Check whether an adjoining district shares your National Character Area, because that scores the full value.
Does the off-site site have to be registered first?
Yes. Off-site gains must be entered on the biodiversity gain sites register maintained by Natural England before they can be allocated to a development, and the biodiversity gain plan cannot be approved without that allocation. Ask for the register reference rather than accepting an assurance that registration is in progress.
How is the 30-year commitment secured?
Either by a planning obligation under section 106 or by a conservation covenant with a responsible body under the Environment Act 2021. Authorities usually prefer a section 106 agreement for land within their own area because they are already a party to it. Both must run for at least 30 years from completion of the habitat works.
What does an off-site biodiversity unit cost?
There is no published national price. Rates depend on habitat type, region and local competition, and figures quoted for one habitat in one county are not transferable. Get written quotes, and weigh the contract terms on condition risk, management funding and insolvency at least as heavily as the headline price per unit.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.