Question: What is Biodiversity Net Gain?
Answer: Biodiversity Net Gain (BNG) is an approach to development that requires habitats for wildlife to be left in a measurably better state than before. Under the Environment Act 2021, most planning applications in England must deliver at least a 10 per cent net gain in biodiversity value, calculated using the Statutory Biodiversity Metric, with the gains secured and managed for at least 30 years.
BNG became mandatory for major developments in February 2024 and for small sites in April 2024, and applies to nationally significant infrastructure projects from late 2025.
Question: Which developments are subject to mandatory BNG?
Answer: Mandatory BNG applies to most applications for planning permission under the Town and Country Planning Act 1990, including residential, commercial and mixed-use development and changes of use involving habitat loss. Exemptions include householder applications, self-build and custom-build developments meeting certain criteria, developments affecting less than 25 m² of habitat or 5 metres of hedgerow, and some biodiversity gain sites. Many Local Plans also apply BNG requirements above 10 per cent.
Question: How is Biodiversity Net Gain calculated?
Answer: BNG is calculated using the Statutory Biodiversity Metric published by DEFRA. The metric converts habitats into biodiversity units based on their area or length, distinctiveness, condition and strategic significance. The pre-development baseline is compared with the post-development habitats, including retained, enhanced and newly created habitats, and separate calculations are made for area habitats, hedgerows and watercourses. Each must individually achieve the 10 per cent gain.
Question: What information must be submitted with a planning application?
Answer: Applications must include:
- A completed Statutory Biodiversity Metric calculation
- A baseline habitat survey using UKHab, with condition assessments
- A plan showing pre- and post-development habitats
- A statement confirming the metric and any degradation of the site since January 2020
- For the post-permission stage, a Biodiversity Gain Plan for approval by the Local Planning Authority before commencement
The Biodiversity Gain Plan is a pre-commencement condition, and works cannot lawfully start until it is approved.
Question: What is the biodiversity gain hierarchy?
Answer: The gain hierarchy requires developers to first avoid impacts on habitats, then minimise them, then restore or enhance habitats on site, then create new habitats on site, and only then use off-site gains or, as a last resort, statutory biodiversity credits purchased from the Government. Planning authorities expect the hierarchy to be evidenced in the Biodiversity Gain Plan.
Question: What are off-site biodiversity units and habitat banks?
Answer: Where it is not possible to achieve 10 per cent net gain on site, developers can purchase biodiversity units from registered off-site habitat banks or secure gains on other land through legal agreements such as Section 106 agreements or conservation covenants. Off-site gains must be registered on the national Biodiversity Gain Sites Register and managed for 30 years. Units closer to the development site and within the same Local Nature Recovery Strategy area score more highly in the metric.
Question: How are BNG habitats secured and managed for 30 years?
Answer: On-site habitat creation and enhancement must be secured by planning condition or Section 106 agreement, and significant on-site gains and all off-site gains require a Habitat Management and Monitoring Plan (HMMP) setting out the management prescriptions, monitoring and reporting for at least 30 years. Developers should consider the long-term maintenance cost and the management company or landowner responsible for delivery.
Question: Why choose Syntegra Group for Biodiversity Net Gain?
Answer: Syntegra Group's ecologists provide the full Biodiversity Net Gain service across England, including UKHab baseline surveys, Statutory Biodiversity Metric calculations, Biodiversity Gain Plans, Habitat Management and Monitoring Plans and advice on off-site units. We work closely with landscape, arboricultural and drainage specialists to design on-site habitats that deliver net gain efficiently and attractively.
We help developers understand the cost and land-take implications of BNG early, avoid pre-commencement delays and satisfy Local Planning Authority requirements.
