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When the UK introduced mandatory Biodiversity Net Gain (BNG) for most developments in April 2024, the goal was ambitious: ensure every new project leaves nature better than it found it. But how is that playing out on the ground?

A group of planning and environmental professionals dug into the details of 503 BNG-compliant planning applications submitted between April and October 2024. Their findings, published in the BNG500 report (March 2025), offer the first detailed snapshot of how developers are responding to the new rules—and what that might mean for the future of land use and nature recovery.

Here’s what stood out.

Most Developers Are Doing More Than the Bare Minimum

67% of the applications proposed to deliver the full 10% biodiversity gain on-site, without relying on offsetting. The median proposed on-site gain was 13%, suggesting many developers are aiming higher than required. Altogether, the average net gain across all projects (including on- and off-site) was 37%.

This might seem surprising, but it reflects a combination of factors—including larger projects like solar farms and mineral sites, which can deliver much higher biodiversity uplift.

Low-Value Habitats Are Being Targeted—As Intended

Most development sites involved habitats of low or medium ecological distinctiveness, with an average baseline biodiversity value of just 3.15 units per hectare. Only 6% of sites included the highest-quality habitats, and these were generally safeguarded within development plans.

This suggests the BNG framework is working as it should: steering development away from ecologically valuable land.

Small Sites, Big Challenges

While small residential developments (<1 hectare) made up 75% of the applications, they were also more likely to struggle with delivering BNG entirely on-site. Many relied on overly optimistic estimates of habitat creation, particularly when assessments weren’t done by professional ecologists.

Still, over time, the quality of these assessments appears to be improving as understanding of BNG grows.

One-Third of Projects Require Off-Site Gains

About 33% of projects needed to source at least part of their BNG requirement from elsewhere, resulting in a demand for around 370 biodiversity units across the sample. When extrapolated nationally, this suggests an annual off-site demand of roughly 7,700 units.

Developers are increasingly turning to habitat banks and other offsetting mechanisms—but many were vague on where or how those offsets would be delivered, hinting at the need for clearer planning guidance and market maturity.

BNG Is Changing the Way We Design Places

One of the more intriguing findings: development is not just preserving biodiversity—it’s often increasing habitat diversity. On average, each project introduced 0.3 more habitat types post-development. Innovative features like bioswales, rain gardens, green roofs, and even green walls were frequently proposed.

This signals a shift toward integrating nature into urban form—not just as an afterthought, but as a design principle.

The System Is Still Maturing—but It’s Promising

While 82% of BNG assessments were done by environmental consultants, the report found some evidence of inconsistent quality, particularly on small sites. That said, the researchers noted fewer examples of “shaky practice” over time.

Regions with strong local policy frameworks—like Oxfordshire—had notably better BNG submissions, suggesting that clear local guidance and experience make a big difference.

What’s Next?

The BNG500 sample paints an encouraging picture. Despite early teething issues, the system appears to be steering development toward better ecological outcomes. As habitat banking markets grow and developers become more familiar with the process, we’re likely to see more effective—and more creative—responses to BNG requirements.

But the work isn’t done. More transparency is needed on where off-site gains are coming from, and small sites in particular need better support and clearer guidance.

Still, it’s not often that we see a planning reform start to shift behaviour so quickly. Biodiversity Net Gain might just be one of the most quietly transformative policies in recent years.