Biodiversity Net Gain: an introduction

Updated: February 2024

Overview


The Government has introduced biodiversity net gain (BNG) as a condition to get planning permission for new development in England.


You must demonstrate that your development increases biodiversity by at least 10%.


BNG became mandatory for large sites on 12 February 2024, and 2 April 2024 for small sites. All planning applications submitted will now need to comply with BNG unless exempt.


The objective of BNG is to provide new homes for the people who need them while protecting and improving nature at the same time. Find out more about the benefits of BNG.

When net gain applies


Small development sites are defined in Article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2015.


There are exemptions in certain situations,  The list of exemptions can be found here: Biodiversity net gain: exempt developments



What level of net gain must you achieve


You need to show that your development will result in a measurable increase in biodiversity of at least 10%. 


Before development, you will need to carry out a baseline survey to measure the existing habitats on the site.


The percentage increase is the total of:

  • the biodiversity within the red line boundary after development compared to the baseline survey
  • biodiversity gains off the site that are registered against the development
  • biodiversity credits bought for the development from the Government.


In some cases, the Local Planning Authority may ask for a percentage higher than 10%.

What steps you must take to demonstrate net gain


You must follow these steps to comply with BNG on your site:

  • calculate the biodiversity value before (baseline survey) and after development using the biodiversity metric.
  • create a Biodiversity gain plan - a document that explains how a project follows the mitigation hierarchy and achieves BNG. You can use the template provided by the Government here. If you are creating significant on-site gains, you may also need to provide a habitat management and monitoring plan (HMMP)
  • submit your metric and biodiversity plan (and HMMP if required) to the Local Planning Authority to discharge the BNG pre-commencement planning condition.
  • deliver the agreed habitat improvements to the required standard for a minimum of 30 years. Onsite delivery will be secured through planning conditions. Landowners will be legally responsible for offsite provision.

How to calculate biodiversity value


You must use the biodiversity metric to measure biodiversity value before and after the development, including for gains provided offsite.


The biodiversity metric calculates an area’s biodiversity value in units. Biodiversity units are based on habitat size, quality, type and location.


You can use the small sites metric for small development sites with little pre-existing biodiversity value.

Find out more about calculating your metric.

A competent person, such as an ecologist, must complete the statutory metric. The Small Sites Metric is developed to be completed by someone familiar with the site; however, you may choose to seek ecological advice.



How you can use units and credits


You must apply the mitigation hierarchy, which means first mitigating losses on the site before considering gains off-site. 


You can either:

  • register units yourself
  • buy units from someone who has registered them against the development on your behalf


Where you use offsite biodiversity units towards your biodiversity gain, you must do both of the following:

  • agree the habitat enhancement under the terms of a planning obligation or conservation covenant
  • record the enhancement in the biodiversity gain site register


You can only buy statutory biodiversity credits from the government as a last resort when onsite and local offsite habitat provisions cannot deliver the required BNG. 


When to consider net gain in your design and build


You should consider how to include biodiversity from the earliest stage of your development. Include BNG when you make decisions about:

  • choosing land to build on, for example, avoiding large woodland areas and protected sites 
  • planning your design and build, so you do not lose biodiversity value during construction 
  • what you spend money on, for example, where and how you can achieve BNG 
  • how you minimise, mitigate or compensate for environmental harm (otherwise known as the mitigation hierarchy) 
  • how you or someone you employ will monitor, report and manage the biodiversity of the site long-term (thorough development of a Biodiversity gain plan an HPPM)
  • how you work with landowners if you do not own the land yourself
  • developing contracts with management companies


Get help and support


Get support from an ecologist

Under the requirement for a competent person to complete the metric appointing an ecologist can help you to:

  • prepare your BNG plan
  • calculate the metric 


Your ecologist can also advise you throughout the process.


Find an ecologist consultant via the Chartered Institute of Ecology and Environmental Management’s directory


Find out more about biodiversity in your area:


Check new standards and best practices:

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