Biodiversity Net Gain (BNG) Assessment
Planning-ready Biodiversity Net Gain assessments that define your baseline, set a practical route to uplift, and keep your project moving with clarity and control — delivered nationwide by experienced ecologists.
When is a Biodiversity Net Gain (BNG) Assessment Required?
A BNG assessment is usually needed for developments requiring planning permission, especially where existing habitats could be affected.
This includes:
- Sites impacting habitats of 25 m²+ or linear features (e.g., hedgerows) of 5 m+
- Residential, commercial, industrial, or mixed-use developments involving site clearance or land use change
- Greenfield or brownfield sites with existing vegetation or ecological value
- Projects involving removal or alteration of trees, scrub, grassland, or hedgerows
- Larger or phased developments, where biodiversity must be assessed across multiple stages
Smaller developments may be exempt if they fall below thresholds and don’t affect priority habitats or protected features, but confirmation early in the planning process is recommended.
Habitat degradation is also considered:
- Sites degraded or cleared since 30th January 2020 are assessed based on their condition before the damage
- This includes both unauthorised works and certain permitted activities that reduce biodiversity value
- Where previous site conditions are unclear, a precautionary approach is applied using the best available evidence
- Applicants must declare prior degradation with supporting evidence and biodiversity calculations
This ensures developments deliver real and measurable biodiversity net gain, preventing artificial reduction of habitat value.
Do you need a Biodiversity Net Gain Assessment?
You’ll need a BNG Assessment if your development falls under the Environment Act 2021 or local planning policy requiring at least a 10 percent net gain.
Most planning authorities now expect clear, measurable evidence that your design will leave biodiversity better than it found it.
Early assessment prevents validation delays, redesign, and seasonal constraints that can stall project schedules.
What is a Biodiversity Net Gain Assessment?
A BNG Assessment quantifies ecological change using the DEFRA Biodiversity Metric 4.0, comparing pre- and post-development habitat value.
It defines a realistic route to achieve or exceed the 10 % requirement through on-site enhancement, off-site delivery, or statutory biodiversity credits.
BNG evidence supports planning validation, mitigation design, BNG Metric 4.0 outputs, and long-term management plans — keeping your project compliant and predictable.
A clear BNG pathway keeps your planning route defensible from first layout to final condition sign-off.
Trigger points — signs your site needs BNG clarity
These indicators suggest your site might require more than a basic walkover and may attract LPA scrutiny:
- New build or major infrastructure projects
- Brownfield redevelopment with habitat value
- Greenfield expansion or edge-of-settlement schemes
- Sites near habitat networks or water features
- Applications referencing BNG in validation checklists
- Local policy or SPD requiring measurable uplift
Early BNG scoping identifies the simplest route to compliance before design is fixed.
How is a BNG Assessment different from a Biodiversity Gain Plan and Habitat Management and Monitoring Plan?
Purpose: quantify biodiversity change
Output: DEFRA Metric 4.0 calculation
When: before design freeze / planning submission
Audience: design teams, planners, ecologists
Depth: technical, evidence-led
Purpose: satisfy the legal BNG condition
Output: statutory-compliant plan for LPA approval and the BNG Register
When: AFTER BNG Assessment, BEFORE permission or condition discharge
Audience: planning officers, legal teams, Natural England
Depth: formal, structured, compliance-focused
Think of it as the difference between calculating the uplift and legally securing it.
Purpose: long-term delivery
Output: 30-year habitat management and monitoring framework
When: after BNG approval, before condition discharge or commencement
Audience: LPAs, ecologists, site managers, long-term stewards
Depth: detailed and operational
What We Deliver
We keep guidance clear and planning-ready — supporting predictable project delivery.
| Service Element | Purpose | Outcome |
|---|---|---|
| Baseline Survey & Habitat Classification | Map and score existing habitats | Verified data for BNG metric |
| DEFRA Metric Calculation | Quantify pre/post development biodiversity units | Transparent 10%+ gain evidence |
| Design Integration | Link layout and landscape plans to BNG targets | Realistic habitat creation plan |
| Mitigation & Enhancement Strategy | Define habitat measures and maintenance | Planning-ready documentation |
| Off-Site or Credit Assessment | Evaluate alternatives if on-site gain is limited | Fully compliant BNG route |
| Monitoring & Management Plans | Secure long-term habitat value | Predictable compliance over time |
How it Works
Our process is designed to remove friction and keep decisions moving.
Scoping & Baseline
Review your layout and context to confirm survey and metric requirements.
Habitat Survey & Mapping
Undertake UKHab classification to map baseline value.
Metric Analysis & Design Input
Calculate unit change and advise on layout adjustments or off-site options.
Reporting & Submission
Deliver a planning-ready BNG report aligned to DEFRA and local policy.
Early alignment between design and metric keeps BNG predictable — not reactive.
Timing & Survey Windows
Early instruction secures the survey window and keeps ecology off the critical path.
That’s how project control is maintained.
BNG integration
Year-round
Follow-on Species Surveys
Seasonal
PEA Survey Season
Year-round
Why planning officers request BNG Assessments
BNG is now embedded in national policy. Without early clarity, LPAs issue validation queries, request redesigns, or defer decisions until BNG deficits are resolved.
Planners expect structured, defensible evidence showing compliance towards:
- Environment Act 2021 — mandatory 10 % net gain
- Town and Country Planning Act 1990 (as amended)
- NPPF Section 15 — Conserve and enhance the natural environment
- DEFRA Metric 4.0 & BNG Guidance
- Local Planning Policy and SPD requirements
Early alignment with these standards ensures your planning authority receives clear, compliant evidence from the first submission — no second rounds required.
Our Approach
ProHort BNG reports are built to meet national and local policy tests, delivered nationwide with clarity and precision. Our reports are written for real-world application, concise enough for planners, and detailed enough for scrutiny.
Planners expect structured, defensible evidence:
- Baseline habitats are accurately classified.
- Post-development design achieves measurable uplift.
- Long-term management is secured.
- Off-site measures or credits are proportionate and costed.
Proactive BNG work demonstrates control, foresight, and credibility. Our methods are transparent and applied consistently nationwide.
That’s how evidence stays proportionate, design stays on schedule, and your programme keeps moving.
How this supports your project
A well-timed BNG:
- Establishes a clear habitat baseline early.
- Prevents planning delays from missing BNG evidence.
- Supports design and layout optimisation.
- Integrates with EIA and Protected Species reports.
- Provides quantified outputs for planning conditions and the BNG register.
Securing BNG early keeps planning and construction timelines predictable.
Case Insight
Your Next Step
Get the ecological clarity that keeps your design on track.
Phone: 0800 494 7479
Email: [email protected]
Areas We Cover
We cover many areas across England and Wales. Click below to find out more.
BNG FAQ - Planning and Programme Clarity
How much does a Biodiversity Net Gain assessment cost?
The cost of a Biodiversity Net Gain assessment typically starts from £850 + VAT for straightforward single plot residential sites with low habitat complexity and clear access.
For sites up to 0.5 acres, costs usually range between £1,000 and £1,500 + VAT, depending on factors such as habitat diversity, the presence of hedgerows or mature trees, and how developed the site layout is at the time of instruction.
Larger sites, phased developments, or schemes with more complex ecological features will require a bespoke quotation. Engaging early in the design process can often reduce overall costs by minimising redesign and additional survey requirements.
What is included in a BNG assessment fee?
A standard BNG assessment is a comprehensive piece of ecological work designed to support your planning application. It typically includes:
- A detailed site visit by a qualified ecologist
- Habitat classification in line with UKHab or equivalent standards
- DEFRA biodiversity metric calculations to establish baseline and post development values
- An impact assessment of the proposed development
- A planning ready BNG report suitable for submission to the Local Planning Authority
This process ensures that your development is assessed correctly from the outset and provides a clear strategy for achieving compliance.
What is not included in a BNG assessment?
A Biodiversity Net Gain assessment focuses on measuring and demonstrating biodiversity uplift at the planning stage. It does not include:
- A Biodiversity Gain Plan, which is required after planning permission is granted
- A Habitat Management and Monitoring Plan, which sets out how biodiversity will be maintained over 30 years
- Design revisions or repeated metric calculations following layout changes
- The sourcing or brokerage of off site biodiversity units
These elements form part of the wider BNG process and are typically commissioned separately as the project progresses.
When does the cost of a BNG assessment increase?
Costs can increase depending on the complexity of the site and the level of input required. This commonly includes situations where:
- Habitat diversity is moderate or high, requiring more detailed assessment
- Hedgerows need formal condition surveys and classification
- The development layout is still evolving, requiring multiple metric iterations
- Additional clarification or revisions are requested by the Local Planning Authority
- The site includes constraints such as protected habitats or ecological sensitivities
Starting the process early, particularly at concept or pre planning stage, can significantly reduce costs by limiting the need for rework.
Is Biodiversity Net Gain mandatory in the UK?
Yes. Biodiversity Net Gain is now a mandatory requirement in England under the Environment Act 2021. Most developments must demonstrate at least a 10 percent increase in biodiversity value compared to the pre development baseline.
This requirement applies to the majority of residential and commercial developments and is enforced through the planning system. Failure to demonstrate compliance can result in planning applications being delayed, refused, or subject to additional conditions.
How is Biodiversity Net Gain calculated?
Biodiversity Net Gain is calculated using the statutory biodiversity metric developed by Natural England.
The metric assigns biodiversity units based on habitat size, type, condition, and distinctiveness. These units are calculated for the site in its existing condition and then compared against the proposed post development scenario.
The aim is to demonstrate a measurable increase of at least 10 percent. The process requires technical expertise to ensure that inputs are accurate and that assumptions align with planning policy and best practice guidance.
How long does a BNG assessment take?
For straightforward residential sites, a Biodiversity Net Gain assessment can typically be completed within 5-10 working days from appointment, assuming access is available and no additional surveys are required.
More complex sites, or those requiring further ecological input, may take longer. Timescales can also be influenced by planning deadlines, site conditions, and the need for coordination with design teams or planners.
Do I need a BNG assessment for planning permission?
In most cases, yes. A BNG assessment is now a key requirement for planning applications in England. Local Planning Authorities expect to see clear evidence that biodiversity net gain has been considered and can be achieved.
Without this information, your application may not be validated or could be delayed while additional information is requested. Including a robust BNG assessment early in the process helps ensure a smoother planning journey.
What is a Biodiversity Gain Plan and when is it required?
A Biodiversity Gain Plan is a formal document that must be submitted after planning permission has been granted but before development begins.
It sets out in detail how the biodiversity enhancements identified in the assessment will be delivered, managed, and monitored over time. The plan must be approved by the Local Planning Authority and forms part of the legal framework ensuring compliance with BNG requirements.
How long does Biodiversity Net Gain need to be maintained?
All biodiversity enhancements delivered as part of a development must be maintained for a minimum of 30 years.
This long term commitment is typically secured through planning conditions, Section 106 agreements, or conservation covenants with a Responsible Body. Proper planning at the assessment stage is essential to ensure that these obligations are realistic, achievable, and cost effective over the full term.
What happens if my site cannot achieve 10 percent net gain?
If it is not possible to achieve the required uplift within the site boundary, alternative solutions must be explored. This usually involves securing off site biodiversity units from a third party or purchasing statutory biodiversity credits.
These options must be clearly justified and agreed with the Local Planning Authority, and they often come at a higher cost than delivering biodiversity enhancements onsite.
Who can carry out a BNG assessment?
A Biodiversity Net Gain assessment should be carried out by a qualified and experienced ecologist.
The process involves technical habitat classification, use of the statutory metric, and an understanding of planning policy and local authority expectations. Errors or omissions can lead to delays, increased costs, or refusal of planning permission, so professional input is essential.
Can a BNG assessment delay my planning application?
Yes, particularly if it is not completed correctly or submitted at the right stage. Missing or inaccurate BNG information is a common cause of planning delays.
Engaging an ecologist early and ensuring that the assessment aligns with your proposed layout can significantly reduce the risk of delays and improve the likelihood of a smooth planning process.
What role does the Local Planning Authority play in BNG?
The Local Planning Authority is responsible for reviewing your BNG assessment and ensuring it meets both national and local policy requirements.
They will assess the biodiversity metric calculations, proposed mitigation measures, and long term management strategy. For example, guidance from Staffordshire County Council and other LPAs will influence how applications are validated and determined.
Is a BNG assessment required for small developments?
Some exemptions exist, such as certain householder applications or developments that fall below defined thresholds. However, the majority of residential and commercial schemes will still require compliance with Biodiversity Net Gain.
It is always advisable to confirm requirements at an early stage, as assumptions about exemptions can lead to delays or complications during the planning process.
