Updated 20 September 2026
No room for nature
Biodiversity net gain means a 10% gain held for thirty years, mandatory since February 2024. A typical East of England register plot is a yard or a car park under half a hectare with no spare ground for habitat, so the gain is bought off-site or the scheme shrinks. From 6 August 2026 the government exempted sites of 0.2 hectares or less altogether, which is close to conceding that the smallest leftover plots cannot carry the duty.
The rule
The Environment Act 2021 and the February 2024 commencement of the biodiversity net gain condition require most development to leave biodiversity 10% better than the baseline, measured in statutory units, and secured for at least 30 years. For major development, Planning Practice Guidance still says on-site delivery should be considered first.
The 2026 amendment regulations then cut the bottom off the duty. From 6 August 2026 a site of 0.2 hectares or less is exempt unless it harms on-site priority habitat, and Defra expects that to remove the requirement from roughly half of the residential permissions that previously carried it. For minor development that remains in scope, off-site gains now rank level with on-site habitat rather than below it.
That is the policy conceding the point this page makes. The smallest previously developed plots were not able to deliver habitat, and the answer was to stop asking them. It does not help the band just above the threshold, which is where a great deal of the East's register sits.
Why brownfield is a poor fit
Previously developed land in the East is usually already covered by buildings, hardstanding or leftover scrub of low distinctiveness. That can make the baseline low, which sounds helpful, until the layout is drawn:
- a 0.3 hectare yard that needs access, parking, bins and a turning head has no room for a 30-year habitat.
- flood storage and drainage already compete for the same leftover corners.
- contamination can make on-site soils unusable as habitat without further cost.
The result is purchased off-site units, or a cut in the number of homes so that a strip of planting can be shown on the plan. The first raises housing cost. The second cuts register capacity again.
Environmental improvement needs space
A planned new settlement can put habitat in from the start and still meet a housing number. A scatter of leftover yards cannot. Treating the brownfield register as the environmental option as well as the housing option asks the smallest, most constrained plots to do two jobs they were not sized for.
How to read the map
The BNG step takes out sites larger than 0.2 hectares and smaller than half a hectare: big enough that the duty still applies, small enough that there is nowhere to put the habitat. Sites at or below 0.2 hectares are exempt and stay in the count, so the map does not claim a discount the law no longer imposes. There are a great many of those, and they average single figures of homes each.
Size is a proxy for on-site habitat capacity, not a statutory test. A larger site that is fully built out can fail in the same way, and this screen will not catch it.
Questions people ask
- Can brownfield sites skip biodiversity net gain?
- Not for being brownfield. Development on a site of 0.2 hectares or less has been exempt since 6 August 2026, and the de minimis and irreplaceable-habitat rules still apply, but a housing scheme above that threshold is not exempt because the land was previously developed. A separate brownfield exemption was consulted on and has not been made.
- Why does this reduce housing capacity?
- On-site habitat takes plot that would otherwise be homes, parking or play space. Off-site units add cost. Either the scheme shrinks or the residual value falls. On the tightest plots both happen.
- What changed in August 2026?
- Three things. Sites of 0.2 hectares or less became exempt. Temporary permissions of five years or less became exempt. And for minor development the hierarchy changed, so off-site gains now sit level with on-site creation instead of below it. The changes apply to applications made on or after 6 August 2026.
Where the numbers come from
- Planning Practice Guidance: biodiversity net gain — Department for Environment, Food and Rural Affairs / MHCLG, 12 February 2024. 10% biodiversity net gain became mandatory for major development in February 2024.
- Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 — legislation.gov.uk, 14 July 2026. SI 2026/790. From 6 August 2026 exempts development on sites of 0.2 hectares or less, exempts temporary development of five years or less, removes the self and custom build exemption, and puts off-site gains level with on-site in the hierarchy for minor development.
- Improving the implementation of biodiversity net gain for minor, medium and brownfield development: government response — Department for Environment, Food and Rural Affairs, 1 April 2026. Government declined to exempt all minor development, and expects the 0.2 hectare exemption to remove roughly half of the residential permissions previously required to deliver net gain. A separate brownfield exemption remains under consideration.
- Environment Act 2021, Part 6 (nature and biodiversity) — legislation.gov.uk, 9 November 2021
- Brownfield land dataset — Ministry of Housing, Communities and Local Government, 20 September 2026. National aggregation of Part 1 registers. Points, not polygons. Coverage may be incomplete. Open Government Licence v3.0.
- Guidance on dereliction, demolition and remediation costs — Homes and Communities Agency, 1 January 2015