Biodiversity Net Gain Surveys required from January 2024

From February 2024 Biodiversity Net Gain Surveys will be a mandatory part of the development of all large residential and non-residential development schemes, with only the smallest development sites exempt from the new regulations.

Under the new rules, most large residential, commercial, and mixed-use construction projects will have to conduct biodiversity surveys and demonstrate a minimum 10% increase in biodiversity value compared to the pre-development baseline. Biodiversity value is measured in standardised biodiversity units using a statutory metric, explained in more detail below. The policy aims to integrate creating and improving natural habitats across the country with the development process and make a meaningful contribution to the decline of nature in the UK.

What is a Biodiversity Net Gain Survey?

A Biodiversity Net Gain Survey, or BNG survey for short, provides a detailed ecological assessment of the current habitat within a development site. A competent assessor (usually a CIEEM registered ecologist) measures the size, condition, and distinctiveness of existing features like ancient trees, woodlands, grasslands, ponds, and hedgerows. They then use the government’s Statutory  Biodiversity Metric to calculate a site’s baseline value in biodiversity units. According to the metric: ‘biodiversity units’ are used to describe relative biodiversity value. The metric considers factors like habitat type, richness, age, connectivity, and rarity on a geographic scale. The metric distinguishes three types of biodiversity units: area habitat units, hedgerow units and watercourse units.

After proposals for the development are drawn up, ecologists will reassess the projected habitat structure and biodiversity units post-construction. This is similar to an Arboricultural Impact Assessment but instead of measuring the impact of the proposed development on the trees, it measures the impact of the proposed development on the site’s biodiversity. If the proposed development plans fall short of a 10% uplift in biodiversity units, further onsite habitat creation or offsite biodiversity enhancement will be necessary before local authorities can grant planning permission.

Developers must also submit a long-term maintenance plan for preserving gains over at least 30 years. Regular ecological monitoring and site inspections will check that enhancements are cared for as agreed and that short-term habitat gains do not lapse over time due to a lack of appropriate stewardship.

Is there a law that says I need a Biodiversity Net Gain Survey?

Yes. Under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021) biodiversity net gain is a mandatory condition of planning permission. At the moment the law only applies to major development projects proposed after January 2024. Major development projects are defined as those proposing more than 9 houses or which build on over one hectare.

Do ALL planning applications for new residential property need a Biodiversity Net Gain Survey?

No, or at least not yet. If your development is between one and nine houses you will not be required to provide any additional biodiversity net gain information with your planning application at this time, however from April the law is set to include these smaller development sites, so it’s a good time to plan for this. For non-residential developments, a small site is considered one where the site area is less than one hectare or where the footprint of the space created is less than 1,000 square meters. There are some additional exemptions to the requirement for a Biodiversity Net Gain Survey detailed on the government’s BNG information pages.


the view over a town which borders potential development land that would require a biodiversity net gain survey to be built on

Does a Biodiversity Net Gain Survey negate the need for other ecological surveys?

No. The use or requirement for Biodiversity Net Gain does not override any existing biodiversity protections, statutory obligations or policy requirements, ecological mitigation hierarchy or any other requirements, for example, a BS5837 survey if you have trees near or on the development site.

Who can undertake Biodiversity Net Gain Surveys?

The first principle of using the new Statutory BNG metric is that it should be completed by a competent person. Their competency must be aligned with the British Standard ‘Process for designing and implementing biodiversity net gain (BS 8683:202)’. We recommend that Biodiversity Net Gain surveys are carried out by a certified ecologist who understands habitat types, protected species and variations in local planning policy regulations across the UK and can also advise whether other ecology surveys may be necessary to support the application.

Where can I find out more information about Biodiversity Net Gain Surveys?

We have lots more information on Biodiversity Net Gain Surveys on our website; take a look at the main Ecology and Biodiversity Net Gain page for a more detailed look at:

  • Measuring Biodiversity Net Gain
  • Ways to achieve Biodiversity Net Gain
  • Maintaining habitats for Biodiversity Net Gain

If you have a specific question related to the implementation of Biodiversity Net Gain legislation this year please contact our expert team who will be happy to assist with your enquiry, either call us directly on 08000 141 330 or use the contact form at the bottom of the page.

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