The disparity in take-up and implementation of BNG across the country

The sector’s response to the requirement for a minimum 10% biodiversity net gain (BNG) has been generally positive. However, there are some inconsistencies and difficulties in how the policy is being applied in practice.

To understand the evolving market, our report, Biodiversity Net Gain: Navigating the Evolving Market, analysed over 3,300 hectares of development sites across England. It found that the average habitat baseline value is 3.45 units per hectare. To secure a 10% net gain on a typical 10-hectare site, developers must enhance or create habitats to achieve at least 37.95 biodiversity units (BUs). If the required 10% uplift cannot be delivered on site, the costs for off-site compensation can quickly escalate and the availability of habitat sites can vary considerably depending on location and habitat type required.

By its very nature, the UK is an ecologically diverse landscape. Ancient woodlands, chalk grasslands and coastal salt marshes are present, as are high-density urban environments, brownfield and heavily constrained sites. As such, there are very different capacities for meeting BNG criteria both on and off-site.

For instance, the East and South East have established habitat banks to enable biodiversity improvements. However, due to the level of housing delivery expected in these regions, the availability of habitat banks will be critical to successful delivery. Elsewhere, off-site opportunities are less common and this is where the effective execution of BNG becomes a more challenging prospect. For affordable and social housing projects, which can be subject to greater financial pressures or limited flexibility, the difficulty can be greater.

There are also significant differences across habitat types. That said, when measuring the biodiversity value of existing land, the contrast between greenfield and brownfield land is not as pronounced as many anticipate. While greenfield sites have an average baseline of 3.60 BU/ha, brownfield sites typically sit at 3.17 BU/ha.

At present, biodiversity units can be sourced from across the country, but with the spatial risk multiplier favouring and supporting local delivery. However, should LPAs begin to press for BNG to be delivered strictly within their own boundaries, the options available to developers will narrow considerably, placing even greater pressure on costs and locations where land and habitat banks are already stretched.

Our report reveals that 54.7% developments are delivering BNG entirely on-site. While this may be within reach on some, it is not always realistic. Where on-site provision is not possible, developers are instead turning to off-site solutions – whether through their own land holdings, the purchase of BUs from third-party providers, or, as a last resort, through the national statutory credit scheme (although evidence suggests the latter option is rarely used, presumably due to the prohibitive costs involved).

Though often viable on larger or less constrained sites, on-site BNG can be less feasible for affordable and social schemes working with tighter budgets and sometimes more heavily constrained sites.

With government targeting an ambitious housing target of 1.5 million homes within five years, demand will inevitably increase. On-site, this may pose issues in relation to density and viability, while off-site, requirements may well exceed supply, at least initially.

If BNG is to fulfil its potential, delivery must be achievable on a national scale, not just where favourable conditions already exist. Strategic coordination will be essential. Without these, disparity will persist, jeopardising much-needed housing delivery, including affordable and social housing, and BNG will risk becoming something of a postcode lottery. A consistent framework, grounded in practicality, is the only route to achieving fair, functional outcomes across the country.

Richard Holliday, associate partner, Carter Jonas (Leeds)