Biodiversity Net Gain - considering a targeted exemption for residential brownfield development

Biodiversity Net Gain (BNG) is an approach to development designed to leave the natural environment in a measurably better state than before development takes place. The Environment Act 2021 introduced a mandatory BNG requirement in England for most new developments under the Town and Country Planning Act 1990, requiring them to deliver a 10% increase in biodiversity. Following a two-year transition period, BNG has been mandatory for most major developments from 12th February 2024, and for minor development (small sites) from 2nd April 2024.

The government is committed to delivering sustained economic growth as set out in our Plan for Change and building 1.5 million homes by the end of this Parliament. At the same time, we are committed to halting and reversing the decline of nature. BNG provides a clear framework to support these objectives, but the early stages of implementation have highlighted challenges for certain types of development. In May 2025, the Government consulted on improving the implementation of BNG for minor, medium and brownfield development, alongside a separate consultation on applying BNG to Nationally Significant Infrastructure Projects (NSIPs).

The Government set out its intention for BNG alongside the publication of the draft National Planning Policy Framework for consultation in December 2025. The responses to these consultations have now been published, and government has confirmed it will be introducing an exemption for sites under 0.2 hectares, as well as other targeted exemptions and simplifications. This includes measures to help address the challenges of delivering BNG on brownfield sites with Open Mosaic Habitat (OMH), an ecologically valuable habitat which can establish on previously developed sites.

The Government also announced it would consult rapidly on options for a potential further exemption to better support brownfield residential development on sites up to 2.5 hectares. This consultation sets out options for this further potential exemption to better support brownfield (previously developed) land coming forward for residential development. This is in line with proposed wider reforms to create a more rules‑based planning system and support housing delivery on suitable urban land.