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Net Biodiversity Gain: The Nuts and Bolts (1 of 2)

Net Biodiversity Gain: The Nuts and Bolts (1 of 2)

Biodiversity net gain


1.  This is the first of a two-part series on the net biodiversity gain provisions set out in the Environment Bill. They would make it a mandatory condition for most development to achieve a 10% biodiversity net gain in order to proceed. 

2.  This first post explains the nuts and bolts of the proposed system, and highlights some of the matters that will be dealt with in regulations (a draft of which has not yet been published). The second post will examine the potential challenges the provisions will create for developers and local authorities and how they might be overcome.


3.  Nationally Significant Infrastructure Projects and marine development would not be subject to the new system. However, it would apply to all development permitted under the Town and Country Planning Act 1990, subject to exceptions.

4.  Exceptions set out in the Bill include generally permitted development and urgent Crown development. Furthermore, the Secretary of State would be given a general power to exempt other categories of development through regulations. 

5.  It is unclear what other categories of development (if any) would be exempted through regulations. The Government consultation response suggests potential exemptions may be created where viability could be a concern, including in relation to small scale, self-build and brownfield development. It is not clear whether viability concerns would be presumed in relation to specified categories or whether this would need to be proven.

The Biodiversity Gain Objective

6.  The requirement to achieve a 10% net gain in biodiversity is called the “Biodiversity Gain Objective”. By default the extent of the net gain is set at 10% although the Secretary of State would be given a power to change the relevant percentage through regulations. 

7.  The developer’s “Biodiversity Gain Plan” (see below) should assess the value of the site’s biodiversity before development and after development, and demonstrate that at least a 10% net gain is achieved between these values.

8.  The development should seek to meet the Objective through improvements on site to biodiversity value where practicable. On-site improvements must be secured through a condition, planning obligation or conservation covenant and be maintained for at least 30 years post-completion.

9.  However, if the objective cannot be achieved through onsite improvements, for feasibility or other reasons, two compensation mechanisms will exist to demonstrate compliance with the Objective. The first involves purchasing off-site benefits achieved on “Biodiversity Gain Sites” and allocating these to the development. Biodiversity gain sites will be registered on a newly established Public Biodiversity Gain Site Register. 

10.  The second involves purchasing “Biodiversity Credits” from central Government.

Calculating biodiversity value

11.  Biodiversity value is to be calculated by applying the “Biodiversity Metric”. This is a tool which the Secretary of State will publish which measures biodiversity value. The DEFRA Biodiversity Metric (the current version of which is dated July 2019) will presumably be adopted for this purpose. 

12.  The Government consultation suggests that the Metric will undergo continual monitoring, review and updating, and comments will be sought on proposed changes before they are implemented.

13.  The relevant date for calculating the “Pre-Development Biodiversity Value” will generally be the date of the planning application. However, the date will be pushed back where activities have been carried out on the site without planning permission which has lowered biodiversity value. Also, where the site is registered as a “Biodiversity Gain Site” (see above), this value is taken as that which the site is expected to achieve.

14.  The Post Development Biodiversity Value is determined by applying the metric to the development plans, which should be explained in the Biodiversity Gain Plan.

The Biodiversity Gain Plan

15.  The steps that are proposed to achieve the Objective must be set out in a “Biodiversity Gain Plan”. It should set out in particular:

a.    The steps taken to minimise adverse effects on onsite habitat;
b.    “Pre-Development Biodiversity Value”;
c.    “Post-Development Biodiversity Value”;
d.    Any registered “Offsite Biodiversity Gain” allocated; and
e.    Any “Biodiversity Credits” purchased for the development.


16.  The administration of the new system will be the responsibility of local planning authorities.

17.  The condition will operate as a general condition imposed on all applicable planning permissions. It would require the submission and approval of the Biodiversity Gain Plan before development commences.

18.  If approval is refused, the development could not proceed lawfully unless there is a successful appeal of the refusal to PINS.

19.  That is all for now. Watch out for the next blog post which will follow shortly…

Horatio Waller is a barrister at Francis Taylor Building.