It has been over a year since the mandatory biodiversity net gain ("BNG") requirement came into force. Here we give a short summary of what we can expect to see going forward.
- Measuring gain
The statutory BNG requirement came into force on 24 February 2024 for major developments, and is expected to come into force in November 2025 for Nationally Significant Infrastructure Projects, having been introduced by the Environment Act 2021. It requires almost all new developments to achieve at least a 10% BNG.
The Department for Environment, Food and Rural Affairs' ("DEFRA") has developed a statutory metric to calculate the biodiversity of a site, using biodiversity units. This metric is used to work out the biodiversity value pre-development, as well as the units required to achieve the required BNG post-development. This gain can be achieved by way of on-site or off-site improvements. This includes the purchase of off-site biodiversity units, as well as through the purchase of statutory biodiversity credits. Any habitat improvements must be maintained for at least 30 years. However, to ensure the gain is achieved as locally as possible to the development, it must be delivered in accordance with the biodiversity gain hierarchy. This states that on-site BNG must be considered first, and only once this option has been exhausted can developers consider off-site BNG.
- Effect of BNG
The quantum of BNG provided on-site is hard to assess, as on-site gain is not recorded nationally, just evidenced via biodiversity gain plans as part of the planning process. It may be that the on-site impact of the BNG requirement becomes more obvious in the next few years as any permitted habitat creation and enhancement starts to be completed.
In comparison, to generate units for off-site BNG, sites producing the gain must be recorded on the Biodiversity Gain Sites Register. This means there is a relatively clear picture of how many sites, so far, have been producing BNG to be able to allocate (and likely sell) to others. According to a blog posted by DEFRA on 12 November 2024, as at that date, there were "19 gain sites on the register, totalling over 500 hectares of habitat".
The last option available to developers seeking to achieve their BNG requirement is through the purchase of statutory BNG credits. The government has set this system up to be an intentionally uncompetitive process and is very much a last resort. The number of developments relying on this option is hard to ascertain as there is no public register for the sale of such credits. Instead the Secretary of State for DEFRA is to publish an annual report detailing how any such monies paid to the government have been spent. A meaningful report in this regard is not expected until the end of this year.
- BNG in practice
There have been some concerns raised that the BNG regime is not delivering enough gain, partly because of the various exemptions. This concern was addressed by DEFRA in a blog in which they supported the exemptions as being proportionate and encouraging "developers to avoid impacting biodiversity in the first place". This is because those sites which are not already biodiverse are often exempt from the requirement.
However, it is too early to tell whether the exemptions are in fact too far reaching as the mandatory BNG requirement only applies to planning applications submitted on or after 12 February 2024. This means that we may not see the true impact of BNG for some years to come. BNG requirements will only demonstrate gain when developments start, so we need to wait for the schemes permitted by applications submitted, and granted, since that date to commence before we can really appreciate the impact. Tough economic conditions may also mean it takes longer for those relatively new permissions to start on site.
Enforcement and penalties
Reputational damage, delays and penalties for failure to comply. Local Planning Authorities can withhold planning permissions, enforce fines or require remediation work if BNG requirements are not met.
Future
As the regime matures, it seems likely that we will see an increase not only in on-site habitat creation and enhancements but also in dedicated BNG sites and portfolio management in a way that optimises BNG.
The Government (MHCLG) has announced a consultation proposing reduced Biodiversity Net Gain requirements for small and medium building developments; this consultation closed on 24 July 2025. We will provide an update as soon as one is available.
For more detail, see this article.