Planning permissions granted under section 73 of the Town and Country Planning Act 1990 are subject to biodiversity net gain (BNG) requirements, but in ways that are not always clearly understood. This insight explains:

• how mandatory BNG interacts with section 73; and
• the differences between single phase and multi-phase developments.

Mandatory BNG regime

Permissions granted where the application was made on or after 12 February 2024 are subject to a statutory condition requiring a local planning authority's approval of a biodiversity gain plan before commencement (the Statutory Condition).

There are some basic rules:

• The Statutory Condition does not apply to any permissions granted under section 73 if permission for the original application was granted before 12 February 2024.
• Subsequent section 73 permissions will remain exempt as long as the original application was made before 12 February 2024.
• For permissions where a BNG plan was already approved, an updated biodiversity gain plan will need to be submitted before commencement under the new section 73 permission where the changes alter the post-development BNG value. (This rule applies whether the post-development BNG value is worsened or improved, so section 73 applications to amend a landscaping scheme secured by condition can expect to trigger a new biodiversity gain plan for approval.)
• If triggered, the new biodiversity gain plan can be submitted with the section 73 application to minimise delays to commencing development under the new section 73 permission.

Mandatory BNG for phased development

A modified regime applies if the permission is:

• in outline and the reserved matter approval has the effect of requiring or permitting development to be carried out in phases; or
• granted subject to conditions having that effect,

(either being a Phased Permission).

Phased Permission will be subject to a condition which prevents development from commencing until an overall biodiversity gain plan has been submitted to and approved by the local planning authority. Additionally, a condition will be imposed which will prevent any phase from commencing until a phase biodiversity gain plan for that phase has been submitted to and approved by the local planning authority. See the Planning Advisory Service's BNG condition template resource for phased development which explains the mandatory regime, its key requirements and provides two options for template conditions.

A local planning authority cannot approve any phase biodiversity gain plan unless it is satisfied that, among other things, the post-development BNG value of the onsite habitat for any phase which has been commenced is at least the value specified in the biodiversity gain plan most recently approved for that phase.

Phased development and section 73 permissions

Where a Phased Permission has been granted under section 73, a previously approved overall or phase biodiversity gain plan will remain approved if, as is the case for non-phased development, the conditions under the section 73 permission do not change the post-development BNG value.

A Phased Permission, however, will be granted subject to an additional condition so that, where permission has been granted under section 73, no further development of an already commenced phase may be carried out unless a:

• phase biodiversity gain plan for that phase has been submitted to, and approved by, the local planning authority; or
• a phase biodiversity gain plan has been previously approved and the conditions of the new section 73 permission do not alter the post-development BNG value.

If a section 73 application would vary the post-development BNG value, the local planning authority need not be satisfied that a phase already commenced has achieved the post-development BNG value.

This blog sets out the regime as if there is no irreplaceable habitat on site. If there is irreplaceable habitat onsite, see the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024 for non-phased development and Biodiversity Gain (Town and Country Planning) (Modifications and Amendments) (England) Regulations 2024/50 for phased development.