Statutory Biodiversity Metric (SBM) Assessments
The Statutory Biodiversity Metric (SBM), sometimes referred to as the BNG metric or the DEFRA biodiversity metric, is the official tool for demonstrating Biodiversity Net Gain (BNG) in planning. It allows developers, planners, and ecologists to calculate a site’s biodiversity units before and after development, using a standardised approach recognised across England.
At ACP Consultants, we specialise in applying the statutory metric calculator/workbook alongside detailed UKHab metric mapping to generate robust evidence. Our outputs feed directly into your Biodiversity Gain Plan (BGP) and Habitat Management & Monitoring Plan (HMMP). By producing planning-ready assessments, we help projects secure approval while contributing to ecological sustainability and wider Sustainable Development Goals.
You can also drop us an email at hello@acp-consultants.com and we’ll get back to you within 24 hours to help with your inquiry!
We follow a simple, transparent process to ensure your project runs smoothly from the very first contact to the final report. Our approach is designed to provide you with clarity at every step, so you’re fully informed and confident in moving forward.
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Step 1: Request a Quote
Fill out our quick quote form or call us, and our team will provide a free, no-obligation quote, outlining the services tailored to your needs.
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Step 2: Confirm Your Booking
Once you approve the quote, simply return the booking form. We’ll schedule your survey and ensure all the details are taken care of.
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Step 3: Receive Your Report
After your survey is completed and payment is received, we’ll promptly issue your survey report, ensuring you get the results as quickly as possible.
What is the Statutory Biodiversity Metric?
The Statutory Biodiversity Metric (SBM) is the official calculation framework published by DEFRA and Natural England to support delivery of Biodiversity Net Gain (BNG). It is the legal standard now required for planning applications, replacing earlier advisory tools such as Biodiversity Metric 3.0.
At its core, the Statutory Biodiversity Metric converts detailed habitat information into measurable biodiversity units. This makes it possible to compare conditions before and after development, and to demonstrate whether a scheme achieves the mandatory 10% net gain in biodiversity value.
The SBM operates across three distinct modules:
- Area habitats: covering woodland, grassland, arable, and urban green spaces.
- Hedgerows: vital for habitat connectivity and landscape structure.
- Watercourses: including rivers, streams, and ditches that support aquatic biodiversity.
Each module scores habitats according to distinctiveness, condition, strategic significance, and connectivity. These scores are then combined into a transparent biodiversity units calculation. By applying this method, developments can be assessed consistently across England, giving planners and developers a clear framework for decision-making.
The statutory package includes three essential components: the statutory metric calculator/workbook (Excel), a detailed user guide, and condition assessment sheets for each habitat type. Together, these provide the technical basis for calculating biodiversity units and ensuring results are robust and repeatable.
By mandating the Statutory Biodiversity Metric, the government has embedded ecological measurement into the planning system, making it a central tool for demonstrating BNG compliance, ecological sustainability, and natural capital outcomes.
When do you need to use the Statutory Biodiversity Metric (SBM)?
The Statutory Biodiversity Metric (SBM) is now required for the majority of planning applications in England. Since Biodiversity Net Gain (BNG) became a statutory duty in 2024, almost all developments must demonstrate how they will achieve at least a 10% net gain in biodiversity value. The SBM provides the transparent framework for proving this to local planning authorities.
The timing of the requirement depends on the type of development:
- Major developments: mandatory from 12 February 2024.
- Small sites: mandatory from 2 April 2024.
- Nationally Significant Infrastructure Projects (NSIPs): scheduled to fall under the duty from May 2026.
To comply, applicants must submit a Biodiversity Gain Plan (BGP) alongside their planning application. The BGP shows how the SBM calculations demonstrate compliance with the 10% uplift and sets out the proposed strategy for delivery and monitoring.
Some very minor projects may be eligible to use the Small Sites Metric (SSM). However, SSM is only permitted where strict eligibility rules are met. It cannot be used if the site contains priority habitats, involves irreplaceable features such as ancient woodland, or requires an Environmental Impact Assessment (EIA).
In all other cases, the Statutory Biodiversity Metric is mandatory. By applying the SBM, developers ensure that their projects are consistent with national policy, provide credible ecological evidence, and contribute to wider nature conservation strategies and green infrastructure development.
Planning & compliance essentials
Applying the Statutory Biodiversity Metric (SBM) is no longer optional — it is a core part of the planning process. Developers and consultants must demonstrate compliance with both Biodiversity Net Gain (BNG) legislation and local planning authority requirements. To do this, it is essential to follow the official framework.
Use the official package
Only the most recent statutory biodiversity metric calculator/workbook, condition assessment sheets, and user guide are valid. Using outdated versions or improvised spreadsheets can lead to planning refusal.
Assess all three modules
The SBM requires separate calculations for area habitats, hedgerows, and watercourses. Skipping a module means the results are incomplete and will not satisfy an LPA.
SSM vs SBM
While the Small Sites Metric (SSM) exists for certain BNG small sites, most projects must use the full SBM. Misapplying SSM is a common error and can cause validation delays.
Irreplaceable habitats
Habitats such as ancient woodland or veteran trees are classed as irreplaceable. Losses cannot be offset through the metric and must be addressed through bespoke compensation outside the calculator.
Biodiversity credits
Government-issued biodiversity credits are available, but only as a last resort when on-site and off-site options are impossible. LPAs will expect evidence that all other options have been explored first.
Long-term securing of gains
Any habitat created or enhanced must be maintained for at least 30 years. This is normally achieved through a Section 106 agreement or a conservation covenant, ensuring delivery is legally binding.
By following these compliance steps, developers can be confident that their SBM assessment is valid, defensible, and contributes to wider green infrastructure development and nature conservation strategies.
Our process
Our approach to the Statutory Biodiversity Metric (SBM) is designed to give developers confidence that their schemes will meet Biodiversity Net Gain (BNG) requirements without unnecessary risk. Each step adds rigour and provides a clear audit trail that planning authorities recognise.
Discovery & constraints
We begin every SBM assessment with a discovery stage. This includes reviewing your red line boundary, masterplan, and ecological constraints. At this stage, we identify whether priority habitats, irreplaceable features such as ancient woodland, or protected species are present. We also consider whether the project may qualify for the Small Sites Metric (SSM), although most developments require the full SBM. Early discovery helps prevent wasted time and ensures the correct metric is used from the outset.
UKHab mapping & baseline units
Our ecologists then carry out detailed UKHab mapping. Habitats are classified, mapped, and condition-scored to establish a baseline biodiversity units calculation. Even though SBM is a structured calculator, the results are only as accurate as the baseline data. Our mapping produces GIS layers, target notes, and habitat polygons that can be validated by LPAs and reused in design iterations.
Design review & the BNG hierarchy
With the baseline established, we work with design teams to apply the BNG hierarchy: avoid → minimise → restore → off-site → credits. This ensures impacts are reduced as far as possible and opportunities for on-site enhancement are maximised. Typical advice includes repositioning infrastructure to protect hedgerows, integrating green roofs or walls, and creating high-distinctiveness habitats such as species-rich grassland. Aligning design with the hierarchy reduces future costs and strengthens the project’s planning case.
Options appraisal: on-site, off-site, credits
We then model scenarios within the statutory biodiversity metric calculator. First, we look at on-site enhancements. If these are insufficient, we explore off-site biodiversity units, ensuring they are properly recorded through the biodiversity gain site register. Only if these options are exhausted do we consider statutory credits, which are deliberately priced as a last resort. This tiered approach demonstrates to LPAs that the project has followed best practice.
BGP & HMMP inputs
The outputs of the metric are then converted into planning documents. We provide structured inputs for your Biodiversity Gain Plan (BGP), which must be submitted post-permission but pre-commencement. We also prepare draft content for the Habitat Management & Monitoring Plan (HMMP), covering monitoring protocols, triggers, and responsibilities. These documents support wider biodiversity management plans and ecological monitoring required by LPAs.
Legal securing & submission
Finally, we advise on the legal securing of biodiversity gains for 30 years. This typically involves a Section 106 agreement or a conservation covenant. We ensure the chosen mechanism is proportionate, enforceable, and aligned with ecosystem services valuation principles. We also remain available to respond to planning officer queries and provide clarifications, helping your application progress smoothly.
In the past year, we’ve delivered over 750 audit-ready reports supporting 400+ projects for developers, planners, and architects nationwide. We put quality over quantity and build lasting relationships based on trust, ensuring your planning applications are backed by robust evidence and delivered on time.
You can also drop us an email at hello@acp-consultants.com and we’ll get back to you within 24 hours to help with your inquiry!
What you get (deliverables)
Commissioning ACP to complete a Statutory Biodiversity Metric (SBM) assessment provides you with a full set of planning-ready deliverables. These outputs give LPAs confidence in your submission and provide you with clear evidence that the mandatory 10% net gain requirement is met.
SBM workbook (Excel)
We complete the official statutory metric calculator, showing pre- and post-development habitat units, with full notes and version control. This is the central evidence document for demonstrating compliance.
UKHab map pack
We supply baseline and proposed UKHab mapping outputs, including GIS files, polygons, and annotated site maps. These make it easy for planning officers to visualise habitat change.
Summary report (PDF)
A concise report explains our methodology, presents results for each module (area, hedgerow, watercourse), and includes an options appraisal. The report is written in plain English for ease of validation.
BGP & HMMP inputs
We prepare structured text, tables, and figures that can be inserted directly into your Biodiversity Gain Plan and Habitat Management & Monitoring Plan. This saves time and ensures consistency between documents.
Quality assurance and version control
All deliverables are quality-checked, version-logged, and aligned with the latest DEFRA guidance. This provides confidence that your evidence will stand up to scrutiny.
Deliverable | Inclusions | Benefit |
SBM workbook (Excel) | Completed statutory metric calculator with inputs and notes | Transparent biodiversity units calculation |
UKHab map pack | GIS layers, habitat polygons, target notes | Evidences baseline and proposed habitats |
Summary report (PDF) | Methods, results by module, options appraisal | Concise, LPA-friendly |
BGP & HMMP inputs | Prepared text, tables, monitoring guidance | Streamlines planning submission |
QA & version control | Version logs and compliance checks | Ensures outputs meet DEFRA standards |
Timelines & costs
The timeframe and cost of a Statutory Biodiversity Metric (SBM) assessment will depend on several factors. Every project is unique, but by setting expectations early we help developers plan effectively and avoid delays.
What affects timescales?
- Site size and complexity: larger or more varied sites take longer to survey and assess.
- Survey requirements: some schemes require extended Phase 1 or detailed UKHab field surveys before the calculator can be completed.
- Design revisions: changes to layouts or landscaping often require recalculating biodiversity units in the metric.
Legal securing: projects that rely on off-site units or need complex Section 106 agreements may extend the programme.
Typical delivery
In most cases, an SBM assessment can be delivered within 2–4 weeks once baseline mapping data are available. For smaller sites eligible for the Small Sites Metric (SSM), the process is often faster. Conversely, large or multi-parcel schemes may take longer, particularly if several iterations of the design are required.
Costs
ACP provides fixed-fee quotes once we have reviewed your red line boundary, layout drawings, and any ecological survey data. Prices vary depending on site size, location, and complexity, but as a guide, SBM assessments typically start from around £399 + VAT.
Budgeting for BNG
It is important to budget for BNG at the same time as other planning requirements, such as land use planning studies and Environmental Impact Assessments (EIAs). Statutory biodiversity credits should only be considered if no on-site or off-site solutions are feasible, as they are priced to be a last-resort measure.
Why choose ACP
Choosing the right consultant to deliver a Statutory Biodiversity Metric (SBM) assessment is critical. At ACP Consultants, we combine technical accuracy with planning insight to give you confidence that your scheme will meet Biodiversity Net Gain (BNG) requirements smoothly.
Planning expertise
Our team has extensive experience engaging with local planning authorities. We understand validation requirements and prepare evidence that speaks the language of planning officers. By presenting clear workbooks and concise reports, we reduce the risk of delays or requests for additional information.
Technical rigour
Every assessment is underpinned by robust UKHab mapping, robust condition assessments, and transparent biodiversity units calculations. We apply ecological best practice to ensure that results are defensible and aligned with the latest statutory biodiversity metric guidance.
End-to-end service
We support projects from the earliest stages of design through to submission and legal securing. Our services cover everything from ecological metrics and biodiversity accounting to preparing text for Biodiversity Gain Plans (BGPs) and Habitat Management & Monitoring Plans (HMMPs). This integrated approach saves clients time and ensures consistency.
Commitment to sustainability
Our work does not stop at compliance. We link BNG delivery to wider sustainability objectives, including the Sustainable Development Goals (SDGs), biodiversity indicators, and the natural capital approach. By aligning your project with these principles, we help demonstrate long-term value.
Trusted partner
All outputs are quality-assured, version-controlled, and tailored to the unique characteristics of each site. That is why developers, architects, and planners trust ACP to deliver reliable results and planning success.
Frequently Asked Questions (FAQs) About the Small Sites Metric (SSM)
The Small Sites Metric (SSM) provides a streamlined way for developers to demonstrate Biodiversity Net Gain (BNG) on minor projects without the complexity of the full Biodiversity Metric 4.0. Designed by Natural England to simplify BNG calculations for small residential and commercial developments, it helps quantify habitat losses and gains where impacts are limited in scale. This FAQ section explains when the SSM can be used, what types of projects qualify, and how to complete it accurately for submission with planning applications. It also outlines the key differences between the SSM and the statutory metric, and how ACP’s ecologists ensure each assessment remains compliant, transparent, and aligned with the latest Defra and Natural England guidance.
How does the Statutory Biodiversity Metric 4.0 differ from Biodiversity Metric 3.0?
The Statutory Biodiversity Metric (SBM) has replaced earlier advisory tools such as Biodiversity Metric 3.0. Unlike those versions, SBM is legally mandated for planning applications. It comes with updated condition sheets, user guidance, and a DEFRA-published workbook. This ensures that biodiversity units are calculated consistently across England and that outputs are fully recognised by local planning authorities.
Should I use SBM or the Small Sites Metric (SSM)?
The Small Sites Metric (SSM) is only valid for very small schemes — typically those under one hectare, with no priority or irreplaceable habitats. If your site contains complex habitats or requires an Environmental Impact Assessment (EIA), the full SBM must be used. ACP can quickly confirm which tool is appropriate so your submission won’t be delayed.
How are biodiversity units calculated?
The statutory metric calculator applies a formula based on habitat size, distinctiveness, condition, connectivity, and strategic significance. Results are expressed in biodiversity units that can be compared before and after development. This transparent biodiversity units calculation makes it clear whether the project achieves the required 10% Biodiversity Net Gain (BNG).
What about irreplaceable habitats?
Irreplaceable habitats such as ancient woodland, veteran trees, and blanket bog are excluded from the metric for impact losses. These cannot be offset using units or statutory credits. Instead, bespoke compensation must be agreed directly with the planning authority and statutory bodies such as Natural England.
Do enhancements need to be secured for 30 years?
Yes. Whether achieved on-site or off-site, all biodiversity enhancements must be legally secured for a minimum of 30 years. This is normally done through a Section 106 agreement or a conservation covenant. Long-term securing provides confidence that ecological gains will be delivered and monitored well beyond the construction phase.
When is a Biodiversity Gain Plan required?
A Biodiversity Gain Plan (BGP) must be submitted after planning permission is granted but before development begins. The BGP sets out how the project will deliver the 10% gain, drawing directly on SBM outputs. It is an essential part of discharging planning conditions under the BNG legislation.
Can statutory credits be used to close gaps?
Yes, but statutory credits are designed to be a last resort. They can only be purchased once it has been proven that neither on-site measures nor off-site biodiversity units can deliver the required gain. Credits are deliberately priced higher to encourage developers to prioritise habitat creation and restoration.
What evidence do LPAs expect with an SBM submission?
Most LPAs expect a comprehensive package including the completed SBM workbook (Excel), UKHab mapping outputs, a concise summary report, and prepared text for the BGP and HMMP. Providing all these documents up front reduces validation queries and improves the chances of swift approval.
Can SBM be used at outline planning stage?
Yes. At outline stage, an initial baseline assessment and indicative post-development calculation can be provided using the SBM. This demonstrates to the LPA that biodiversity has been considered early. Final figures must then be confirmed and resubmitted at reserved matters stage once designs are fixed.
How does SBM link to Environmental Impact Assessment (EIA)?
For projects requiring an EIA, SBM results complement the ecological assessment. By expressing habitat changes in unit terms, the metric provides a quantitative basis for describing impacts and mitigation. This strengthens the overall nature conservation strategy and helps address cumulative effects.
How does SBM link to Environmental Impact Assessment (EIA)?
For projects requiring an EIA, SBM results complement the ecological assessment. By expressing habitat changes in unit terms, the metric provides a quantitative basis for describing impacts and mitigation. This strengthens the overall nature conservation strategy and helps address cumulative effects.
What common errors occur in SBM calculations?
Typical errors include misclassifying habitat distinctiveness, failing to record condition accurately, or double-counting hedgerow trees. Another common mistake is relying on outdated metric versions instead of the current statutory workbook. ACP’s quality assurance process prevents these pitfalls and ensures your outputs are compliant.
Can SBM results be challenged by LPAs?
Yes. LPAs will often scrutinise the assumptions behind the metric. If mapping, condition assessments, or units are not clear, they may request additional information. Using a consultant who provides transparent UKHab mapping, clear assumptions, and version control helps minimise the risk of challenges.
Government Guidance and Statutory References
- Statutory framework & planning condition – Biodiversity Net Gain under Schedule 7A of the Town and Country Planning Act 1990; statutory regime explained in Planning Practice Guidance (GOV.UK).
- Biodiversity Gain Plan – Must be approved before commencement; Local Planning Authority decision normally within 8 weeks. See Biodiversity Net Gain Guidance (GOV.UK).
- Statutory biodiversity metric – How units are calculated, modules, factors, and guidance on early use. Statutory Metric and User Guide (GOV.UK).
- Condition Sheets & Small Sites Metric (SSM) – Official metric tools and guidance sheets. BNG Metric Tools (GOV.UK).
- Exemptions & de minimis thresholds – Householder, small self-build, and very small impacts where no priority habitat is affected. Exemptions Guidance (GOV.UK) and Defra Environment Blog.
- Off-site register & fee – Natural England guidance on registering biodiversity gain sites, with the current £639 registration fee. Register a Biodiversity Gain Site (GOV.UK).
- NSIPs timing – Government proposals indicate that BNG will apply to Nationally Significant Infrastructure Projects (NSIPs) from May 2026, pending final regulations. Defra Consultation (GOV.UK).
- Creating a Habitat Management & Monitoring Plan (HMMP) – GOV.UK guidance on how to prepare HMMPs, including monitoring and reporting requirements. HMMP Guidance (GOV.UK).
- Natural England HMMP Template (JP058) – Official template, checklist, and monitoring report tools for Habitat Management & Monitoring Plans. Natural England Publications.
- Statutory Biodiversity Metric User Guide (July 2025) – Full guidance on how the statutory metric should be applied, including trading rules and worked examples. User Guide PDF.
- Metric Supporting Documents (JP039) – Includes GIS templates, data standards, and case studies for applying the statutory metric. Natural England Publications.
- Statutory Biodiversity metric user guide.
Other Supporting References (Quick Links)
- BNG in Practice Report (2025) – Case studies showing how BNG is being delivered in real projects. Institute of Environmental Sciences.
- Biodiversity Net Gain – Principles and Guidance for UK Construction and Developments. Chartered Institute of Ecology and Environmental Management.
- BNG Research Briefing – This post note outlines the mandatory biodiversity net gain policy introduced in England in 2024 and the risks and challenges for delivering its objectives. UK Parliament.
- Biodiversity net gain: where to start. Natural England.
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Next Steps
Need a Statutory Biodiversity Metric (SBM) assessment for your project? Send us your red line boundary, layout drawings, and any ecological reports. We’ll confirm the right approach, timescales, and provide a fixed-fee proposal for planning-ready delivery.
Explore Related Biodiversity Net Gain Resources
The Statutory Biodiversity Metric 4.0 is the foundation of every Biodiversity Net Gain (BNG) calculation, translating habitat data into measurable biodiversity units. To understand how this metric fits within the national framework, start with the Biodiversity Net Gain Overview and the BNG Legislation & Guidance explaining how the Environment Act 2021 makes use of the metric mandatory.
For smaller developments, see how the Small Sites Metric (SSM) offers a streamlined alternative. Once calculations are complete, document outcomes using the Biodiversity Gain Plan (BGP) and Habitat Management and Monitoring Plan (HMMP). Our BNG Templates & Downloads provide standardised forms for recording metric results.
For delivery and verification, use the BNG Monitoring Fee Calculator and explore Off-Site Biodiversity Units or Registering a Gain Site to secure long-term ecological uplift. You can also review BNG Case Studies & Portfolio to see how metric outputs are implemented successfully in practice.
You can also drop us an email at hello@acp-consultants.com and we’ll get back to you within 24 hours to help with your inquiry!
- Last Updated:
- October 2025
Disclaimer: Our content is prepared by ACP Consultants’ in-house specialists and is based on current guidance, standards, and best practice in environmental consultancy. While we make every effort to keep information accurate and up to date, it is provided for general guidance only and should not be relied upon as a substitute for professional advice on specific projects. Planning authorities retain final decision-making powers, and requirements may vary between local authorities and over time. ACP Consultants accepts no liability for any loss arising from reliance on this content without obtaining tailored advice for your project.