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21 February 20225 minute read

Environment Act 2021

Biodiversity Net Gain under the Town and Country Planning Act 1990
Developers need to be aware of the provisions relating to Biodiversity Net Gain (BNG) contained in the Environment Act 2021 (Act), which was given Royal Assent on 9 November 2021.

The Act contains provisions for the protection and improvement of the environment, including in relation to air quality, waste, water and biodiversity. Of immediate interest to the development industry is the legal requirement to provide BNG (previously a policy requirement in the National Planning Policy Framework). While the law isn’t in force yet, it already has implications for the viability of development proposals.

We await full detail of how BNG will work, but a recent consultation has set out further information on how the BNG provisions may apply. This article outlines proposals for how BNG requirements will apply to development, in England only, under the Town and Country Planning Act 1990 (1990 Act).

Deemed Planning Condition

The Act introduces a series of amendments to the 1990 Act. These provide for the inclusion of a deemed planning condition on every planning permission in England, subject to certain limited exceptions. This condition will stop commencement of development until a BNG plan has been submitted to and approved by the local planning authority. The BNG plan must set out how the “Biodiversity Gain objective” is met. Since it is a statutory provision, developers won’t be able to avoid it.

Biodiversity Gain Objective and the Metric

The “Biodiversity Gain objective” is that the biodiversity value attributable to a development must exceed the pre-development biodiversity value of site by at least 10%. This percentage may be amended by regulations, but change is not currently proposed. This is a statutory requirement that cannot be contracted out of. In addition, it appears some local planning authorities are considering introducing local policies seeking a higher percentage; where such policies are adopted, development proposals must comply to secure planning permission, unless there are valid planning reasons to make an exception in a particular case.

The pre-development biodiversity value of a site is the biodiversity value of the onsite habitat on the date of the planning application. However, if any activity on the site after 30 January 2020 degrades the onsite biodiversity, and was not authorised by a planning permission, the pre-development biodiversity value will be as the value existing immediately before the activities were carried out.

Biodiversity value will be calculated in accordance with a biodiversity metric (measured in terms of “biodiversity units”). The metric currently developed for these purposes is the Biodiversity Metric 3.0, issued by Natural England in 2021. 

Securing post-development BNG

The post-development biodiversity value of a development includes:

  • the value of the onsite habitat of the completed development;
  • the biodiversity value of registered offsite BNG units allocated to the development; and
  • the biodiversity value of any biodiversity credits purchased (the consultation points to this option being a last resort).

Any offsite BNG units must be secured through a conservation covenant or planning obligation, and be maintained for at least 30 years. The consultation envisages that offsite works should be started as soon as possible, and not more than 12 months after discharge of the BNG condition. It remains to be seen how this will operate – for example, where implementation of the development is not required in this timescale.


There are current exemptions to the BNG requirement, but these are limited to permitted development granted permission by development order; and urgent crown development.

The consultation proposes further exemptions for householder extensions, small development (below a de minimis threshold), change of use applications, self-build housing and the creation of BNG sites, which only enhance biodiversity.

However, even where there is an exemption, the consultation points out this exemption from mandatory BNG would not prevent planning authorities requiring biodiversity gains on exempted developments in line with local or national planning policy.

What next?
  • Be prepared. The consultation suggests that the provisions should be in force within two years of the Act coming into force (ie November 2023).
  • Remember. Unless the development falls into an exemption, the deemed condition requiring a BNG plan can’t be avoided. Even where there is a statutory exemption, planning policies requiring BNG will still need to be addressed in planning applications.
  • Note. 30 January 2020 is the date for measuring baseline biodiversity value of sites where activities carried out don’t have planning permission.
  • Be aware. BNG policies are already being drafted into some local plans, and the requirements to avoid degradation of onsite biodiversity mean the impacts of these policies will already bite on development sites.
  • Respond. Send your thoughts on the proposals set out in the consultation by 5 April 2022.

If you have any questions about the potential implications of the BNG regime under the 1990 Act for your business, please contact Amy Truman, a legal director in our Planning and Land Use team.