The Government has published Biodiversity Metric 4.0, expected to be the metric eventually adopted for the purposes of calculating biodiversity net gain ("BNG") as required by the Environment Act 2021. It is anticipated the obligations will come into force in November 2023 for larger sites, and smaller sites will be subject to phased introduction expected to follow in April 2024. 

The metric is used to assess the biodiversity unit value of an area of land and therefore can demonstrate a net gain, or loss, consistently. A separate metric is applicable to smaller sites. 

Delivering the required 10% BNG offsite will be available if it is not possible to provide it on the development site itself. The metric inherently incentivises offsite enhancements located close to the development site, over those located further away. As a result, the further away the offsite delivery from the development site, the more biodiversity units required in order to deliver the required gains. 

Natural England has indicated it will continue to work with the Government on improving the metric, with an understanding that major updates will arise every 3-5 years. On the assumption Metric 4.0 is formally adopted, there will clearly be a period of transition whilst developers and local authorities adjust to the new requirements of the planning regime which will no doubt lead to the metric being revised. 

Working on the basis that BNG obligations and the associated planning conditions will become mandatory in November 2023, developers and land managers can prepare by calculating the biodiversity value of intended development sites in advance.