7 Essential Steps in Your Biodiversity Net Gain - BNG Process Guide

In England, the requirement for Biodiversity Net Gain became mandatory for new planning applications from late 2023 under the Environment Act 2021. Specifically, as of 12 February 2024, most major developments need to deliver at least a 10% net gain in biodiversity, with small developments following from 2 April 2024. (Wales, Scotland, and Northern Ireland have their own approaches, but the 10% mandate applies to England.)

Certain types of developments are exempt. These include small-scale works that impact very limited habitat areas (for example, under 25 m² of habitat loss or under 5 m of hedgerow), householder applications like home extensions, and some self-build projects meeting specific size criteria. Nationally significant infrastructure projects have a later start date for BNG (NSIPs will require net gain from 2025/2026). Additionally, urgent works by Crown bodies and developments covered by permitted development rights are exempt. Always check the latest government guidance to see if an exemption applies.

A biodiversity gain plan is a document that a developer must submit (usually as a condition of planning permission) detailing how the project will achieve the required net gain in biodiversity. Under the new rules, the biodiversity gain plan is typically prepared after planning permission is granted but before development begins. It must outline the pre-development biodiversity value, the habitat enhancements on-site, and any off-site gains or credits to reach the 10% net gain. There is a standard template for this plan, and planning authorities will review it to confirm the BNG objective is met before allowing works to commence.

Biodiversity units are calculated using the Statutory Biodiversity Metric tool provided by Defra/Natural England. Ecologists input data on each habitat’s area, type, condition, and location into the metric. The metric applies a formula (with multipliers for factors like risk and distinctiveness) to determine the habitat’s biodiversity unit value. The same process is used to calculate post-development units for proposed new or enhanced habitats. The 10% net gain requirement means the total post-development units must be at least 10% greater than the total pre-development units. For example, if a site has 100 biodiversity units before development, the design must deliver at least 110 units after development. The metric ensures consistency in how gains and losses are quantified across projects.

The mitigation hierarchy is a guiding framework in biodiversity planning that prioritises how to handle impacts. The steps are: Avoid impacts first (e.g. redesign the project to protect important habitats), Minimise impacts that can’t be avoided (reduce harm through measures like careful timing of works), Restore on-site where damage occurs (rehabilitate habitats that were disturbed), and as a last resort Offset or Compensate for any residual impacts off-site. BNG builds on this by requiring an overall positive outcome after all these steps. In practice, you must demonstrate that you’ve tried to avoid and minimise harm as much as possible before resorting to off-site compensation or credits. BNG is an additional gain on top of making good any unavoidable losses.

Yes, in cases where on-site and local off-site options are insufficient, developers can purchase statutory biodiversity credits from the government as a last resort. These credits fund strategic habitat projects elsewhere. However, credits are intended to be a fallback option. Preferably, the net gain should be achieved through on-site habitat creation or enhancement, or by arranging off-site units via a conservation partner. Credits can be costly and they typically deliver benefits outside the immediate area of your development, so planning authorities encourage developers to use credits only when absolutely necessary.

By law, any habitat created or enhanced to deliver BNG must be maintained for a minimum of 30 years. This is secured through legal agreements such as Section 106 planning obligations or conservation covenants. In practice, that means the developer or landowner is responsible for funding and carrying out management (e.g. habitat management, monitoring, invasive species control) for at least three decades after completion of the development. Some projects may opt for even longer management periods to ensure habitats mature and continue to provide biodiversity benefits well into the future.

If monitoring finds that the habitat enhancements are not establishing as planned (for example, tree plantings die off or a created meadow isn’t reaching the intended condition), then corrective actions are required. The Habitat Management and Monitoring Plan will include contingency measures such as replanting vegetation, adjusting management techniques, or additional interventions to address such issues. The legal agreements tied to BNG (like planning conditions or covenants) give authorities the ability to enforce these requirements. In short, the developer remains responsible for making sure the promised net gain is delivered. The 30-year maintenance obligation means there is a long-term duty to remedy problems and ensure the net gain outcome is achieved and sustained.

BNG is designed to complement existing environmental protections, not replace them. Developers must still follow all laws on protected species and habitats (for instance, obtaining licences if bats or great crested newts are present) and carry out any required Environmental Impact Assessment (EIA) for large projects. BNG comes into play after those steps, adding an extra requirement to leave nature better than before. In practice, you would incorporate BNG measures alongside your mitigation for protected species. Often, the biodiversity gain plan will reference mitigation from the EIA (like habitat creation for a protected species) and then add further enhancements to reach net gain. Think of BNG as building upon the foundation of “no net loss” ensured by traditional mitigation, pushing towards a positive outcome for biodiversity.

Yes, several helpful resources are available. Defra has published a biodiversity gain plan template which developers can use to provide all the needed information in a structured way. Natural England offers a set of HMMP tools (Habitat Management and Monitoring Plan templates, checklists, and a habitat management guide, known as Joint Publication JP058) to plan the long-term maintenance of sites. The Statutory Biodiversity Metric tool (currently Metric 4.0) is available as a calculator spreadsheet, accompanied by a detailed user guide. Industry bodies like CIEEM also provide guidance documents and training on BNG. Using these standard templates and tools is highly recommended, as they align with official requirements and make it easier for planning authorities to review your plans. An experienced ecology consultant will be familiar with them and can ensure all documents are correctly completed.

The BNG timeline in the UK generally follows four key phases: pre-application (baseline surveys and metric calculations), planning (preparing and submitting the biodiversity gain plan), delivery (implementing on-site habitat creation or enhancement), and long-term management (monitoring and reporting over at least 30 years). Developers should use Defra’s BNG User Guide alongside the Statutory Biodiversity Metric to ensure each stage is completed correctly. Where on-site improvements cannot fully achieve the required 10% gain, biodiversity offsetting may be used this involves delivering additional habitat gains off-site or purchasing biodiversity credits to meet the shortfall. Following this structured process ensures projects achieve measurable and lasting biodiversity benefits in line with UK regulations.