Understanding when developers should start looking for off site BNG units is critical to achieving compliance under the biodiversity net gain (BNG) framework introduced by the Environment Act 2021. Early engagement is not simply good practice it directly affects planning timelines, cost certainty, and access to suitable off site biodiversity units.
This guide sets out the practical stages at which off site BNG should be considered, and how it fits within the wider planning permission and biodiversity gain plan process.
Start at the Pre-Application Stage
Developers should begin considering off-site units as soon as a scheme enters feasibility or pre-application.
At this stage, your ecologist will:
- Assess existing habitats within the red line boundary of the development site
- Use the statutory biodiversity metric tool to establish baseline site biodiversity units
- Model proposed habitat enhancement and on-site BNG scenarios
This early application of the biodiversity metric helps identify whether development impacting existing biodiversity can be mitigated on site, or whether off site gains will be required.
If a shortfall is likely, you should begin exploring the off site market without delay.
Before Designing Final Layouts
Waiting until the detailed design is complete often creates avoidable risk. The availability of off-site habitats, particularly those aligned with local nature recovery strategy priorities and strategic significance, can influence site layout decisions.
Early consideration allows you to:
- Balance on site and off site BNG units efficiently
- Avoid over-reliance on statutory biodiversity credits (a last resort)
- Ensure alignment with local planning authority expectations
At this stage, developers should begin asking:
- How many biodiversity units are required?
- Do areas or specific features of the site have higher levels of biodiversity?
- What types of habitat units (e.g. grassland, woodland, watercourse units) are needed?
- Are suitable gain sites available within the relevant local area?
Prior to Planning Submission
A biodiversity gain plan must demonstrate how a development will achieve BNG, including any reliance on off site solutions.
While you do not need to have fully purchased biodiversity units at submission, you should:
- Have a clear strategy for delivering off site gains
- Categorically state whether there is an intention to utilise off site BNG
- Identify potential gain site register entries or providers
- Understand how units will be legally secured (e.g. via Section 106 or conservation covenants)
Failure to address this early can delay validation or approval by the local authority. Including the above details gives the local authority a chance to comment on your planned mitigation while proposals are more adaptable: before a consented layout is fixed.
Before Discharge of Planning Conditions
BNG becomes a formal planning obligation, and units must be secured before development can lawfully commence.
At this point:
- Off site BNG units must be allocated from a registered biodiversity gain sites register entry
- The arrangement must be backed by a legal agreement with a responsible body or local planning authority
- Associated monitoring plans and habitat management commitments must be in place
Only once these requirements are satisfied will the biodiversity gain plan be approved.
Why Early Engagement Matters
Delaying engagement with the off site BNG process can create several risks:
- Limited availability of suitable off site habitats within the required geography
- Misalignment with local nature recovery strategy priorities
- A need to alter proposals and layouts later in the project timeline
- Increased costs in the private market for BNG units
- Greater reliance on statutory credits, which are intentionally priced as a last resort
- Programme delays where units are not legally secured in time
Early planning ensures access to a broader pool of habitat banking opportunities and supports more efficient environmental management outcomes.
Key Considerations When Sourcing Off-Site Units
When assessing off site biodiversity units, developers should consider:
- Cost
- Ecological quality and alignment with priority habitats
- Compliance with trading rules (habitat type and location)
- Registration on the biodiversity gain sites register (via Natural England)
- Long-term habitat management and habitat enhancement works
- Avoidance of double counting across nature markets (e.g. carbon or nutrient neutrality)
- Delivery of wider environmental benefits, including support for climate adaptation and nature recovery
At Civity
At Civity, we support developers at this early stage by reviewing outputs from the statutory biodiversity metric, identifying any shortfall in biodiversity units required, and advising on suitable off site BNG units available through our landbank.
We do not carry out site-level ecological surveys or replace your ecologist. Instead, we work alongside your project team to:
- Confirm how many units are needed
- Match requirements to registered gain sites
- Allocate units that are fully legally secured and compliant with planning requirements
Summary
Developers should start looking for off site BNG units at the earliest feasible stage—ideally during pre-application and before finalising site design. This ensures that any shortfall in biodiversity net gain can be addressed in a controlled, compliant, and cost-effective way.
By aligning early with the biodiversity metric, engaging with the off site market, and planning for legal agreements and registration requirements, developers can secure appropriate off site solutions and avoid delays to planning permission.
Ultimately, early engagement supports not only compliance but the delivery of meaningful biodiversity gain and long-term improvements to the natural environment.
