To meet the 10% biodiversity net gain (BNG) requirement, a development in England has three delivery routes — enhance habitat on-site, buy registered off-site units, or buy statutory credits from government — and planning law expects you to use them in that order. Choosing the wrong route, or choosing it late, is one of the most expensive mistakes a small developer can make.
This guide compares the three routes as they stand in 2026, including how the spatial risk multiplier quietly inflates off-site purchases and why statutory credits are priced to hurt.
The BNG hierarchy: on-site first, off-site second, credits last
Mandatory BNG under the Environment Act 2021 follows the biodiversity gain hierarchy. Your biodiversity gain plan must show the statutory metric calculation and demonstrate that on-site enhancement was considered before off-site units, and off-site units before statutory credits. Councils check the narrative, not just the numbers — a plan that jumps straight to credits without evidencing the search for alternatives risks refusal of the gain plan.
Route 1: on-site BNG units
On-site delivery means creating or enhancing habitat within the red line: species-rich grassland instead of amenity turf, native hedgerows, wildlife ponds, tree planting. Its advantages are real — no purchase cost, landscape and amenity value, and no multiplier penalties. The commitments are equally real:
- Significant on-site enhancements must be secured and managed for 30 years, usually through a planning condition or section 106 obligation with a habitat management and monitoring plan;
- Habitat must be deliverable — a shaded strip behind plots rarely achieves the condition scores the metric assumes;
- On a tight small site, giving up developable area may cost more than buying units.
For most small schemes the practical answer is a hybrid: deliver what the landscape design genuinely supports on-site, then top up off-site.
Route 2: off-site biodiversity units and the spatial risk multiplier
Off-site units are bought from habitat banks and landowners whose sites are legally secured and recorded on Natural England's Biodiversity Gain Sites Register. Two rules shape the purchase:
- Like for like or better. Under the trading rules, the habitat you buy must be of equal or higher distinctiveness than the habitat lost.
- The spatial risk multiplier. The statutory metric discounts units delivered far from your site. Units within the same local planning authority area (or national character area) count in full; units further afield are discounted, so you must buy more of them to deliver the same gain. Buying local is not just good practice — it is cheaper.
Market prices vary widely by habitat type and region, but off-site units are normally far cheaper than statutory credits, which are deliberately priced above the market.
Practicalities matter on this route too. The seller's site must already be legally secured (by a section 106 agreement or conservation covenant) and registered before your gain plan is approved; allocations are recorded against your specific planning permission; and demand is uneven across the country, so in some authority areas the local supply of the habitat type you need is thin. Start conversations with habitat banks at pre-application stage, not after decision — a signed heads of terms with a local bank is persuasive evidence in a biodiversity gain plan.
Route 3: statutory biodiversity credits — the deliberate last resort
If you can show that neither on-site delivery nor off-site units are available, you may buy statutory credits from government. Two design features make this the route of last resort:
- The 2:1 ratio. Two credits are required for every one biodiversity unit of shortfall;
- Premium pricing. Under the price schedule current since 2 June 2026, credits start at £42,000 (tier A1 habitats such as modified grassland) and rise through £48,000 (A2), £66,000 (A3) and £125,000 (A4) to £650,000 (A5), with hedgerow credits at £44,000 and watercourse credits at £230,000 — before the 2:1 ratio is applied.
Run your own numbers with our free BNG credit cost calculator, which has the 2026 statutory prices built in.
Choosing your route in 2026 — and the rule changes to watch
Before committing to any route, confirm BNG applies to you at all: regulations laid in July 2026 exempt development on sites with a red-line area of 0.2 hectares or less (unless priority habitat is affected) from 31 July 2026, and BNG becomes mandatory for nationally significant infrastructure projects from November 2026. For sites that remain in scope, the sensible sequence is: run the metric early, fix the landscape design around deliverable on-site habitat, get quotes from local habitat banks before the gain plan is drafted, and treat credits purely as a contingency.
How Fortress Associates can help
Fortress Associates prepares planning sustainability statements for every UK local authority. The report is free, is generated in minutes, and covers the 10% biodiversity net gain requirement under the Environment Act 2021 alongside water efficiency (the 110 litres per person per day Part G calculator), urban greening and BREEAM where required. Contact us to discuss your site, or browse our other planning report services.
Sources & further reading
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