Brownfield and BNG: what the data shows (Oct 2026 update)

Back in June, the government consulted on whether brownfield developments should get a special exemption from Biodiversity Net Gain (BNG). To help everyone understand the picture, we looked at the data from Verna’s Mycelia software – the country’s largest dataset on BNG.

We’ve now updated this analysis with another four months’ worth of data. The detailed results are below, but the main conclusion hasn’t changed: Brownfield developments generally find it easier and cheaper to deliver BNG, compared to other development types. Most brownfield schemes voluntarily go significantly beyond 10% BNG, and fewer than 1 in 10 brownfield developments pay for off-site Biodiversity Units. In general, brownfield developments are complying straightforwardly with BNG, and creating benefits for people and nature.

Our latest results are based on data for more than 19,000 developments, drawn from more than 100 Local Planning Authorities (LPAs) across roughly half of England. The data included 2,489 brownfield developments, 96% of which were under 2.5 hectares.

1. Brownfield achieves net gain more easily than other development types

The median on-site net gain on brownfield sites is 39%, three times the 13% median across other development types.

For every Biodiversity Unit (BU) lost on a brownfield site, 1.9 BUs are created or enhanced on-site.

Most brownfield schemes voluntarily exceed the 10% statutory minimum, and by a wide margin.

2. Brownfield schemes rarely need the off-site market

Across all site sizes, brownfield schemes use off-site BUs about half as often as other developments (5–7% of brownfield schemes, compared with 10–13% of other developments).

3. Most of a brownfield site’s biodiversity value sits in a small part of the land lost

Across all brownfield developments, 76% of the habitat area lost was sealed or artificial surface with no biodiversity value.

The majority of a brownfield site’s biodiversity loss is typically concentrated into just 14% of its footprint, and mostly accounted for by four habitat types: Open Mosaic Habitat (OMH), vacant or derelict land, bare ground, and urban trees.

4. Open Mosaic Habitat is very rare

OMH is one of the harder habitats to assess and to compensate for, so it can present challenges for developments where it occurs.

However, it is extremely rare. Only 0.9% of brownfield sites in our database have recorded OMH. Even including those sites where Mycelia’s ecological risk analysis suggests a possibility of unrecorded OMH, the maximum number of brownfield developments potentially affected is less than 3%.

Extrapolating our data to the national picture, OMH-affected brownfield sites are likely to number fewer than 50 per year across the whole of England.

5. Creative urban features do real work

About 15% of the brownfield schemes used creative urban features: green roofs, biodiverse sustainable drainage, bioswales, rain gardens and green walls.

Where they appear, these features deliver a median of around a quarter of the scheme’s net biodiversity uplift.

So, do brownfield developments face particular challenges from BNG?

Over successive analyses, our data shows a consistent answer to this question: No.

In fact, brownfield schemes generally find BNG easier and cheaper to deliver than other developments. Most brownfield schemes voluntarily go significantly beyond 10% BNG, and fewer than 1 in 10 brownfield developments pay for off-site Biodiversity Units.

In general, brownfield developments are complying straightforwardly with BNG, and creating benefits for people and nature.

The real challenges are likely to be where Open Mosaic Habitat is present, but this is rare: likely no more than 50 sites per year across the country.

If the ecology and policy community wants to ease brownfield development whilst enhancing nature and communities, identifying and supporting these few sites is likely to deliver net benefits.

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