Biodiversity Net Gain (BNG)

Biodiversity is the variety of all living things on our planet, from species, habitats and ecosystems. 

Biodiversity Net Gain (BNG) is an approach to planning and land management that leaves the natural environment in a better state than it was before. 

We are committed to protecting and conserving the natural environment, and BNG is at the forefront of our planning system so that habitats within Buckinghamshire can be protected for years to come. 

Why it is important 

Biodiversity Net Gain is important because: 

  • the natural environment provides benefits to us all, and is essential for the processes that support life on this planet 

  • many habitats are lost or degraded by development, and there are limited measures in place to value, maintain, enhance and create wildlife habitats 

  • it delivers measurable improvements for biodiversity by enhancing or creating new habitats in association with development 

You can read further information on the importance of biodiversity on the Royal Society website and the Convention on Biological Diversity website. 

You can also read the Biodiversity Net Gain Brochure on the Natural England website for an overview of BNG and its benefits. 

How it is measured 

BNG is calculated using a biodiversity metric, which measures the biodiversity value of habitats in ‘biodiversity units’ as a proxy for nature. 

The metric can be used to calculate how a development might change the biodiversity value of a site. It can help you to design, plan and make land management decisions that better support biodiversity. 

It uses changes in the extent, distinctiveness and condition and habitats, and compares the biodiversity value of habitats found on a site before and after development to determine if there is a loss or gain in biodiversity. 

There are 4 key factors that underpin this comparison: 

  • habitat size 

  • condition 

  • distinctiveness 

  • location 

See the guidance about using the biodiversity metric on GOV.UK. 

You can also download the latest version of the biodiversity metric and guidance from Natural England. 

What we are doing to deliver BNG 

From November 2023, all planning permission granted in England, with a few exceptions, will have to deliver a minimum of 10% BNG under the Environment Act 2021. 

Between now and November 2023, we are requesting that certain planning proposals demonstrate at least a net gain in biodiversity as measured with the biodiversity metric in line with the requirements of Policy NE3c of the Milton Keynes Local Plan (Plan:MK).

Our local plans provide more information on the relevant local planning policies, and you can find further information in our Biodiversity Supplementary Planning Document. 

The requirement for Biodiversity Net Gain does not alter existing requirements and protections for the natural environment such as protecting important habitats and species. These must be achieved alongside providing BNG. 

Mitigation hierarchy 

Gains in biodiversity should be achieved on-site (within the proposed development site) and this should be a key consideration when designing development proposals. 

This falls in line with the principle of the mitigation hierarchy that is embedded in national planning policy, where the impact on biodiversity must first be: 

  • avoided, then 

  • minimised, then 

  • compensated for on-site 

Only as a last resort, and if compensating for losses on-site is not possible, then biodiversity losses should be offset by gains off-site. 

Offsetting biodiversity losses 

Biodiversity offsets are conservation activities that produce a measurable increase in biodiversity value at a site and are designed to compensate for any remaining losses in biodiversity caused by a proposed development. These are in addition to any avoidance and mitigation measures that have already been implemented to reduce biodiversity loss. 

Biodiversity offsets should be used as a last resort. In certain cases, they are not appropriate and should not be used. 

They are only available for developments that have rigorously applied the mitigation hierarchy and must follow national government BNG principles and rules including being as local to the site of impact as possible. 

They should also be located somewhere of strategic significance to ecology, for example where they help wildlife to move through the landscape by providing a connective corridor or buffering an existing wildlife site. 

Ecology planning consultations

Ecology planning consultations contact information