Updated June 2026 — prices reflect 2026 market conditions
BNG Monitoring Survey Company: UK and London Guide
Since February 2024, major developments must deliver at least 10% Biodiversity Net Gain (BNG). Choosing the right monitoring survey company ensures your development meets statutory requirements and remains compliant throughout the 30-year management period.
What Is Required for BNG Compliance
Mandatory 10% Biodiversity Gain: Developments must deliver at least a 10% increase in biodiversity value compared to pre-development baseline.
| Requirement | Details | | --- | --- | | Applicability | Major developments (more than 9 houses or more than 1 hectare) since February 2024; small sites (1–9 houses or less than 1 hectare) from April 2024 | | Competent assessor | CIEEM-registered ecologist must conduct surveys | | Statutory metric | Natural England's Biodiversity Metric 4.0 (Defra Statutory Biodiversity Metric) | | Legal securing | Habitats must be legally secured for minimum 30 years via S106 agreement or conservation covenant | | Habitat Management and Monitoring Plan (HMMP) | Must detail monitoring activities, management, and adaptive management for 30 years |
Leading BNG Monitoring Survey Companies (UK)
| Company | Services | Notable | | --- | --- | --- | | ACP Consultants | BNG surveys, Biodiversity Gain Plan, HMMP, Metric 4.0 compliance | Fixed fees from £349 for small sites; 1-week turnaround | | Maydencroft | 30-year BNG monitoring, habitat condition surveys, GIS mapping | Adaptive management approach; reports for planning authorities | | Native Ecology | CIEEM Registered Practice; full ecology services for small to large developments | UK-wide | | ECOassistance (Kent and South East) | BNG baseline surveys, QGIS mapping, metric calculations | From £950 for small sites including survey and desktop search | | Elite Ecology | BNG assessments, calculations, habitat management, monitoring | UK-wide coverage | | The BNG Guy | Ecology consultancy, BNG metric calculations, habitat banking | Midlands-based, licensed ecologists |
To find a CIEEM-registered consultant: Use the CIEEM Registered Practices Directory.
Monitoring Frequency and Trigger Levels
Monitoring Schedule
| Period | Frequency | | --- | --- | | Years 1–5 | Annual surveys | | Years 5–30 | Surveys at 5-year increments (years 5, 10, 15, 20, 25, 30) |
Key monitoring points: Typically years 1, 3, 5, 10, 15, 20 as specified in the S106 agreement.
Trigger Levels
- Trigger levels for remedial action are site-specific and defined in the HMMP
- Must specify conditions requiring intervention if habitat condition falls below target
- Include adaptive management responses for different trigger scenarios
What a BNG Monitoring Survey Includes
| Deliverable | Details | | --- | --- | | Habitat condition assessment | UK Habs condition categories A, B, C, D | | Biodiversity Metric calculations | Using Natural England Biodiversity Metric 4.0 | | Condition monitoring reports | Annual or 5-year reporting to LPAs | | GIS mapping | Spatial data for habitat boundaries | | Photographic record | Baseline and ongoing condition documentation | | Trigger level compliance report | Assessment against HMMP thresholds |
2025 UK Costs for BNG Monitoring
| Service | Cost Range (ex VAT) | | --- | --- | | BNG baseline survey (small site) | £950–£2,500 | | BNG baseline survey (medium site) | £2,500–£5,000 | | BNG baseline survey (large site) | £5,000–£15,000+ | | Annual monitoring visit | £500–£2,000 per visit | | 5-year condition survey | £1,500–£5,000 | | Biodiversity Gain Plan preparation | £1,000–£3,000 | | HMMP preparation | £1,500–£4,000 |
London premium: Expect 10–20% higher in London due to site complexity, ecology expertise availability, and planning authority requirements.
Questions to Ask a BNG Monitoring Company
- "Are you CIEEM-registered?" — Required for statutory BNG compliance
- "What is your experience with Biodiversity Metric 4.0?" — Ensure current version knowledge
- "Can you prepare the Biodiversity Gain Plan?" — Required for planning submission
- "What is your monitoring schedule?" — Confirm years 1–5 annual, then 5-yearly
- "What trigger levels do you set?" — Site-specific thresholds for intervention
- "Can you provide GIS mapping?" — Increasingly required by LPAs
- "What is your 30-year commitment?" — Confirm long-term availability
- "Do you have experience with my LPA?" — Local authority-specific requirements vary
BNG vs. Traditional Ecological Survey
| Aspect | BNG Monitoring Survey | Traditional Ecological Survey | | --- | --- | --- | | Purpose | Long-term habitat condition monitoring | One-time ecological assessment | | Duration | 30 years minimum | Single survey | | Compliance | Statutory under Environment Act 2021 | Usually voluntary or planning condition | | Metric | Biodiversity Metric 4.0 calculation | Qualitative assessment | | Trigger levels | Defined in HMMP for ongoing compliance | Not applicable |
Frequently Asked Questions
Q: When did BNG become mandatory?
BNG became mandatory for major developments (more than 9 houses or more than 1 hectare) in February 2024. Small sites (1–9 houses or less than 1 hectare) follow from April 2024.
Q: Who can conduct BNG monitoring surveys?
Surveys must be conducted by a CIEEM-registered ecologist. Use the CIEEM Registered Practices Directory to find qualified consultants.
Q: How long does BNG monitoring last?
A minimum of 30 years — habitats must be managed and monitored for at least 30 years after development completion.
Q: What happens if habitat condition falls below trigger levels?
The HMMP defines site-specific trigger levels and required adaptive management responses. If triggered, remedial action must be taken within agreed timeframes.
Q: Can the same company do baseline and monitoring surveys?
Yes — using the same company throughout ensures consistency in methodology and data. Many companies offer ongoing monitoring contracts.
Q: Is BNG monitoring required for all developments?
Major developments: mandatory since February 2024. Small sites: mandatory since April 2024. Exemptions apply for certain development types — check with your ecologist.