Biodiversity Net Gain Explained for Developers

Biodiversity Net Gain (BNG) is now a central consideration for developers across the UK. Since its mandate in 2024, it has ensured that development projects leave biodiversity in a better state than before. Increasingly, it is likely that a Local planning authority (LPA) will require BNG as part of planning permission conditions.

Understanding BNG is important for both small sites and larger development projects, helping developers meet legal requirements while contributing to long-term ecological improvements.

Biodiversity Net Gain refers to the mandatory concept that, once a development is complete, the ecological value of the site is greater than it was beforehand. Achieving this often involves habitat creation, enhancement of existing habitats, and long-term management to sustain gains.

The impact is measured using the statutory biodiversity metric tool, which converts habitats into biodiversity units. This allows planners and developers to quantify losses and gains for local authority monitoring. Projects must meet the net gain requirement, demonstrating that biodiversity improvements are both measurable and maintainable over time.

In England, BNG is applied as an expected condition of planning permission. While some small sites may be exempt, many local authorities now expect developers to include BNG considerations regardless of project size.

BNG can be delivered on-site, off-site, or using a combination of both approaches. Gains are usually required to be maintained for a minimum of 30 years, secured through planning conditions or a legal agreement. Early engagement with an LPA helps ensure that your biodiversity gain plans align with local requirements and reduce the risk of delays.

A successful BNG strategy requires careful planning and integration into the design process. There are multiple approaches:

• On-site habitat creation – Enhancing existing habitats or creating new ones directly on the development site. This can include planting woodland, establishing wetlands, or installing green roofs.
• Off-site habitat provision – In some cases, developers may invest in biodiversity improvements elsewhere, purchasing or creating off-site BNG units to meet requirements.
• Statutory biodiversity credits – Developers can purchase statutory biodiversity credits from the government-approved schemes to offset ecological losses when direct habitat creation is not feasible.

Effective management and monitoring plans are critical. BNG is not a one-time activity; the gains must be maintained, and the site must be monitored to ensure compliance with the agreed targets.

The monitoring and reporting of Biodiversity Net Gain is structured and evidence-based. A typical process includes:

1. Baseline assessment using the statutory biodiversity metric tool
   The pre-development value of the site is calculated using the DEFRA-issued statutory biodiversity metric tool. This establishes the number of existing biodiversity units and provides a clear starting point.
2. Assessment of predicted losses and gains
   The metric is used to assess potential losses arising from the proposed development and to estimate the biodiversity units that will be delivered through mitigation or habitat creation.
3. Preparation of a Biodiversity Gain Plan
   Developers prepare a clear BNG plan to accompany the planning application. This sets out how the net gain requirement will be achieved, whether on-site, off-site, or through statutory biodiversity credits.
4. Securing commitments through planning conditions or legal agreements
   Local planning authorities typically secure BNG delivery through planning conditions or a legal agreement, ensuring gains are maintained for the required period.
5. Long-term management and monitoring
   Ongoing management and monitoring are implemented to ensure biodiversity units are delivered and maintained over time, providing assurance that the net gain target is met.

Taken together, this process ensures that Biodiversity Net Gain is not only calculated during the application stage, but delivered, secured and maintained throughout the delivery of a project.

Collington Winter Environmental provides practical guidance to help developers navigate BNG requirements. We work with clients to produce clear, evidence-based biodiversity gain plans, ensuring that developments meet LPA expectations while enhancing habitats and species.

We can assist with ecological surveys and desk studies; develop on-site and off-site habitat creation strategies; prepare BNG assessments using the statutory biodiversity metric tool; and advise on long-term management and monitoring to maintain biodiversity units over time. By integrating ecological expertise early in the design process, we help developers reduce the risks involved in modern-day project planning, avoid unnecessary delays, and deliver projects that meet both local and wider environmental objectives.

If you are preparing a planning application or need advice on Biodiversity Net Gain requirements, contact Collington Winter Environmental today via email at info@collingtonwinter.co.uk to discover how a member of our ecological planning team can support your development project.