Biodiversity Net Gain -January 2024 Update

From January 2024, it is mandatory for major developments to deliver at least 10% biodiversity net gain (BNG), as set out in the Environment Act 2021.

As mentioned in our blog on this topic last year, this was originally planned to become mandatory in November 2023. However, the Government delayed the requirement to January 2024, with smaller sites needing to demonstrate a Biodiversity Net Gain (BNG) from April 2024.
Now that this is a mandatory requirement for major developments and is being rolled out to smaller sites later in Spring, we are here to explain what this means for developers and landowners.


BNG is the approach to development and land management that aims to leave the natural environment in a measurably better state than it was before development.
The impact of a development will be measured by an ecological mitigation hierarchy and will need to be secured for at least 30 years.
BNG can include new wildflower meadows, tree planting, hedgerows, ponds, native species rich planting and so on.
For qualifying developments, planning applications will need to show a 10% net gain in biodiversity will be achieved on or off site, through the submission of a biodiversity gain plan.


With the BNG requirement being phased by the Government, we have provided the timeline below to help show when certain developments will need to deliver BNG.

January 2024:

It is now mandatory for major developments to demonstrate a 10% Biodiversity Net Gain when a planning application is submited.
This includes development as defined in the Town and Country Planning (Development Management Procedure) (England) Order 2015:

  • the winning and working of minerals or the use of land for mineral-working deposits;
  • waste development;
  • 10 or more dwellings or where the number of dwellings to be provided is not known, a site area of 0.5 hectares or more.
  • A building or buildings where the floor space to be created by the development is 1,000 square metres or more; or
  • where the site having an area of 1 hectare or more.

April 2024:

The requirement for smaller sites to achieve BNG comes into force in April 2024. Smaller sites comprise of:

  • Between one and nine dwellings or where the number of dwellings to be provided is not known, a site area of less than 0.5 hectare;
  • A building or buildings where floor space to be created is less than 1,000 square metres OR where the site area is less than one hectare.
  • development that is not the winning and working of minerals or the use of land for mineral-working deposits
  • development that is not waste development


It is expected that the requirement for National Infrastructure Delivery projects to deliver BNG will come into force in 2025.


There are certain developments which are exempt from the requirement to demonstrate BNG under the Environment Act 2021, these include:

  • Developments that do not affect a priority habitat and impacts less than 25sqm of habitat, or 5m of linear habitats such as hedgerows;
  • householder applications (such as home extensions, conservatories, loft conversions, new garages and so on);
  • self-build and custom build, provided that the site is no larger than 0.5 hectares, comprises no more than nine dwellings and meets the criteria for self or custom-build housing;
  • developments undertaken for the purpose of fulfilling a BNG planning condition for another development; and
  • Development forming part of or ancillary to the high-speed railway transport network.


It is vital to engage with a qualified ecologist at an early stage of the design process, to ensure that the design incorporates BNG into the overall scheme.
Achieving BNG is a complex process that requires expert input from a suitably qualified ecologist. An ecologist will use the ‘Defra biodiversity metric’ to calculate the existing biodiversity value of habitats on a site before development and then the proposed value following development.
The before and after biodiversity values of the site then need to be measured, to meet the required 10% increase.
This process has already become an integral part of the planning process for major projects and will soon apply to most minor developments.

If you want to know whether BNG will affect your development and you are unsure of the process involved, please get in touch with us today and we would be happy to discuss.

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