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Biodiversity Net Gain: what you need to know.

What is Biodiversity Net Gain?

Biodiversity Net Gain, or BNG, is the practice of leaving our landscape in a better condition than we found it in. As part of the government’s 25 Year Environment Plan new legislation requires developers to achieve 10% BNG, which means that a 10% increase of the baseline biodiversity value of the site must be reached following the development. This can be achieved by delivering biodiversity gains onsite, offsite, purchasing BNG Units and finally, purchasing Statutory Credits.

It applies to Major and Minor Developments

A minor residential development is any development that creates nine dwellings or fewer, or where the dwelling number is unknown, a site area of less than 0.5 hectares.

A minor commercial development is any development creating less than 1000 square metres of floor space or the site area is less than 1 hectare.

Above these thresholds, the development is classed as major.

Important Dates

For Major Developments, 10% BNG will be mandatory on all planning applications submitted after 12 February 2024. For Minor Developments, 10% BNG will be mandatory on all planning applications submitted after 2nd April 2024. 

How is biodiversity measured?

The simplified process:

  • The baseline value is measured by the existing habitats and their condition being classified by a suitably experienced ecologist.

  • Units are then assigned to each distinct area by the Statutory BNG Metric produced by DEFRA.

  • The proposed habitats and condition states are then entered into the Statutory Metric and the units are calculated.

  • The difference between the baseline units and proposed units is calculated.

  • If the difference is below a 10% gain and no more units can be achieved in the proposed layout, the remaining units must be gained through offsite habitat enhancement or creation on land owned by the applicant, purchased through a habitat bank of an individual supplier, or purchased from the government.

Can I reduce the value of my site before starting the application process?

With the new measures many people are wondering if there is a way to reduce the value of their site before beginning the survey process, this might include ploughing, re-surfacing, scrub clearance, tree felling etc.


However, measures have been set out within Schedule 14 of the Environmental Act that allows a planning authority to recognise any degradation to a site after the 30th of January 2020 and take the earlier state of the habitat as the baseline. This can be achieved through aerial imaging and local data sets, if it is not clear what the habitat type or condition is through these methods the highest possible value will be applied. The implications of this are extreme; you may have had a moderately valuable habitat before degradation, but if this cannot be proven it is likely to be recorded as a high-value habitat.


We therefore strongly advise against attempting to reduce the value of your site before having the baseline value of your land calculated.

What is the predicted market for BNG Units?

The need for units purchased from off-site suppliers is expected to be worth £135 million – £274 million annually. The implications of this are twofold: developers and householders need to consider BNG from the outset before they even begin to design their proposed development with an architect, and landowners can begin producing credits ready to supply to the BNG market.

Clarifying Units vs Credits

BNG Units are the measurement of biodiversity value, these are lost and/or created on a development site and landowners can create BNG Units by improving their habitats. Landowners can then sell these units to developers who cannot achieve 10% BNG onsite. The Government BNG Units are called Statutory Credits, these are intended to be the last resort if the 10% target cannot be achieved in another way.

What else do I need to know?

How you apply the knowledge above will vary slightly depending on your project or position. We've prepared specific guidance for the main scenarios below:

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