How to Achieve Biodiversity Net Gain on Your Development

How to achieve Biodiversity Net Gain on your development

Achieving Biodiversity Net Gain means designing, securing and delivering a measurable improvement in habitats, rather than adding a planting schedule to a finished layout. For most in-scope development in England, the minimum statutory target is 10%. The route to that target depends on the existing habitats, the proposed impacts, the applicable trading rules and the feasibility of long-term management.

At Collington Winter Environmental, we bring ecological assessment and landscape thinking together early. This helps identify what should be retained, where habitat improvement is realistic and whether off-site provision is likely to be needed. It also helps avoid promises that look satisfactory in a calculation but cannot be delivered within the site's physical or operational constraints.

Key takeaways

• Confirm whether mandatory BNG applies before setting the project strategy.
• Establish a defensible habitat baseline before clearance or layout decisions.
• Apply the biodiversity gain hierarchy, prioritising avoidance and on-site opportunities.
• Test designs through the statutory metric, including separate habitat accounts and trading rules.
• Secure delivery, management and monitoring before relying on proposed gains.
• Obtain approval of the biodiversity gain plan before development starts.

Step 1: confirm scope and programme requirements

Mandatory BNG began for major development on 12 February 2024 and small development on 2 April 2024, subject to exemptions and transitional rules. Review the application date, permission route, development category and any earlier permissions. A householder application, qualifying self-build scheme or genuinely de minimis proposal may have a different statutory position from another project of similar size.

Our guide to whether biodiversity net gain is mandatory explains the principal tests. Even when exempt, a proposal may still need ecological surveys or measures under other legislation or local policy. Scope those requirements at the same time, while keeping their legal basis clear.

Build surveys, design review, off-site searches and legal work into the programme. Seasonal survey constraints and third-party negotiations can affect the critical path. Treating these as early workstreams provides more options than trying to resolve an unexpected shortfall immediately before construction.

Step 2: establish and protect the baseline

Commission habitat mapping and appropriate condition assessments. Record habitat boundaries, areas or lengths, relevant features and survey limitations. The baseline should be clear enough for the planning authority to understand how the metric inputs were derived and how they correspond with the drawings.

Check for priority and irreplaceable habitats, designated sites, protected species and features requiring specialist assessment. These may influence the developable area before any BNG arithmetic is undertaken. Watercourses, for example, can need specialist condition assessment and careful consideration of effects outside the channel itself.

Do not clear or simplify the site in an attempt to reduce its baseline. Statutory provisions can require earlier habitat value to be used where degradation has occurred. Keeping dated records, photographs and management information supports a transparent assessment and reduces uncertainty about the appropriate starting point.

Step 3: use the hierarchy to improve the layout

The statutory biodiversity gain hierarchy begins with avoidance and then mitigation for adverse effects on on-site habitats of medium distinctiveness or above, before moving through compensation options. Good design also considers avoiding unnecessary losses elsewhere on the site. Review alternative positions for buildings, access roads, services and construction compounds.

Retaining a feature on a drawing is not enough if construction would damage its roots, alter its water supply or isolate it from surrounding habitats. Allow appropriate protection areas and consider the future use of adjoining spaces. Habitat retention should remain credible through construction and occupation, not simply during the planning assessment.

Next, identify realistic enhancement opportunities. Improving the management of retained grassland or hedgerows may be more dependable than creating a demanding habitat on unsuitable ground. On-site creation should serve ecological functions and connect with retained features where possible. The wider approach is explained in our introduction to BNG.

Step 4: calculate the design and check the rules

Use the statutory biodiversity metric, or the Small Sites Metric where its development and ecological eligibility criteria are met. The statutory metric published in January 2024 provides the mandatory framework; use the applicable current tool and guidance for the submission. Do not substitute an old voluntary calculation merely because a project previously used it.

The assessment considers habitat distinctiveness, condition and strategic significance, together with area or length. New or enhanced habitats are subject to relevant time and difficulty adjustments. On-site proposals should reflect realistic target conditions, establishment periods and management, rather than optimistic entries chosen to reach 10%.

Check the following before accepting the result:

• Does each parcel match the baseline and proposed habitat plans?
• Are area habitat, hedgerow and watercourse accounts all addressed where relevant?
• Do gains satisfy the trading rules for the habitats being lost?
• Are retained habitats genuinely protected from direct and indirect impacts?
• Are habitat creation assumptions compatible with drainage, soils, shade and future land use?

Our guide to biodiversity metric calculations explains these checks and includes a clearly hypothetical worked example.

Step 5: make on-site habitats buildable and manageable

Translate habitat proposals into specifications that contractors and managers can use. Define soil preparation, establishment methods, planting or seed requirements, protection, timing and aftercare. Avoid assuming that every green space can achieve a high-value habitat condition while also functioning as a heavily used recreation area.

Sustainable drainage features may contribute where their habitats meet the metric's criteria, but engineering requirements and maintenance access need to be compatible with the ecological target. Likewise, species-rich grassland needs an appropriate cutting or grazing regime and suitable nutrient conditions. A label on a plan does not demonstrate either.

Coordinate ecology drawings with landscape, engineering and utility plans. Late changes to attenuation, levels or service routes can remove the very habitat area needed to meet the target. Set a process for checking design revisions and updating the metric before revised drawings are issued.

Step 6: resolve any off-site requirement

If the compliant on-site result falls short, identify suitable off-site gains. These may come from land controlled by the developer or from a third-party habitat bank. Compare the exact unit types, habitat trading compatibility, delivery status, legal security and geographic relationship to the development.

The spatial risk multiplier can reduce the credited contribution of more distant off-site provision. Watercourses use different spatial considerations from area habitats and hedgerows. Confirm the calculation before agreeing the purchase quantity. A cheaper nominal unit is not necessarily a better compliance option if more units are needed or the habitat trade is unsuitable.

Off-site gains must be secured, registered on Natural England's Biodiversity Gain Sites Register and allocated to the development. Read how habitat banking works for the landowner side of that process. Government statutory biodiversity credits remain the last resort; they should not be confused with normal off-site unit purchases.

Step 7: secure documents and gain plan approval

The planning application should include the required baseline information and a credible explanation of the intended route to compliance. For an in-scope permission, the general biodiversity gain condition means development cannot begin until the planning authority approves the biodiversity gain plan. Phased schemes need the relevant overall and phase documentation.

Prepare legal agreements and management documents early enough to support that approval. A Habitat Management and Monitoring Plan should set out the works, responsibilities, targets and monitoring programme. Significant on-site enhancements and off-site gains require appropriate minimum 30-year arrangements, with the legal mechanism matched to the delivery route.

Review the gain plan against the actual permission, final metric, registered allocations and approved drawings. Consistency matters: an off-site purchase cannot resolve a mismatch between the proposed habitat plan and the workbook, or remove the need to comply with other planning conditions.

Step 8: deliver, monitor and respond

Brief the construction team on retained habitat protection, ecological supervision and the sequence of works. Record completion of habitat creation and enhancement, including any changes from the specification. Handover information should reach the people responsible for estate management, grounds maintenance or off-site land management.

Monitoring should measure progress towards the stated habitat targets, not merely confirm that planting happened. If establishment fails, identify the cause and implement agreed corrective measures. Weather, invasive plants, inappropriate mowing or altered drainage may require changes in management. Long-term success depends on funded responsibilities and practical intervention, rather than assuming that nature will automatically follow the original drawing.

Legal security, management and evidence

Biodiversity gains need more than a planting schedule. Significant on-site habitat enhancements and registered off-site gains must be secured for a minimum of 30 years. For off-site gains, the period runs from completion of the habitat enhancement works. Delivery arrangements should identify the land, the management obligations, the responsible parties, the monitoring programme and the remedies if habitat targets are missed. A section 106 planning obligation or conservation covenant can secure off-site delivery. Conservation covenants are agreements with designated responsible bodies; they are not simply private promises between a seller and buyer.

A Habitat Management and Monitoring Plan, often called an HMMP, translates the ecological proposal into practical tasks. It should describe the starting condition, intended habitat, establishment work, annual management, monitoring methods and measurable milestones. It should also explain how management will change if monitoring shows that the habitat is not developing as expected. Funding, access rights and responsibility after a land sale deserve attention before the documents are signed.

Registration is not the same as ecological approval

Natural England operates the Biodiversity Gain Sites Register for off-site gains. Registration and allocation link secured habitat gains to a development, helping prevent the same units being allocated twice. Register entry does not replace the developer's responsibility to demonstrate compliance, the local planning authority's approval of the biodiversity gain plan, or the land manager's duty to deliver the habitat. Ordinary on-site gains are not registered through this off-site register.

Read the metric alongside wider environmental duties

BNG does not replace protected-species legislation, designated-site protection, environmental assessment or other planning requirements. A scheme can show a numerical uplift and still be unacceptable because it damages an important ecological feature or fails another legal test. Irreplaceable habitats, such as ancient woodland, have special arrangements: losses are not compensated through ordinary metric trading, and bespoke compensation does not make an otherwise unacceptable loss acceptable.

Local Nature Recovery Strategies provide important spatial context. Where applicable, their mapped priorities inform strategic significance in accordance with metric guidance. They can also help identify better-connected habitat projects, but do not automatically make any planting scheme suitable. We consider ecological function, practical management and planning evidence together rather than treating the spreadsheet as the whole assessment.

Talk to our ecologists

Call 01204 939 608 or send us a message using the form on this page for an initial discussion about your site.