BNG Monitoring Survey in London: What You Need
Biodiversity Net Gain (BNG) monitoring in London is mandatory for nearly all developments under the Environment Act 2021. Understanding what is required, when to monitor, and what it costs helps you plan compliance and avoid costly surprises during the 30-year management period.
What Is Required for BNG in London
| Requirement | Details | | --- | --- | | Minimum gain | At least 10% biodiversity net gain compared to pre-development baseline | | Legal agreement | Section 106 agreement or conservation covenant securing habitat for 30 years minimum | | Habitat Management and Monitoring Plan (HMMP) | Must be submitted with the Biodiversity Gain Plan — includes monitoring schedule, management strategy, and reporting protocol | | Biodiversity Gain Plan | Submitted and approved by LPA before construction starts |
Responsibility for implementing and monitoring BNG sits with the determining planning authority — in London, this is typically the borough council.
Monitoring Schedule
Monitoring reports are typically required at these intervals over the 30-year period:
| Year | Milestone | | --- | --- | | Year 2–3 | First monitoring report | | Year 5 | Second report | | Year 10 | Third report | | Year 20 | Fourth report | | Year 30 | Final report |
The exact schedule is specified in your HMMP and legal agreement. Some boroughs may require more frequent reporting in early years.
Deliverables for BNG Monitoring
| Deliverable | Details | | --- | --- | | Annual or biennial monitoring reports | Submitted to the LPA | | Site visit records | Habitat condition assessments | | Photographic evidence | Of habitat establishment and condition | | Updated biodiversity metric calculations | Showing maintained or enhanced units | | Management action records | Grazing, mowing, invasive species control |
Reports go to the planning authority (LPA), register operator (for off-site gains), and responsible body (for conservation covenants).
LPA Requirements in London
London boroughs may have specific expectations beyond the national requirements:
| Aspect | Requirement | | --- | --- | | Pre-application | Draft HMMP with planning application; preliminary ecological appraisal (PEAR) | | City of London | Target: 3.0 biodiversity units per hectare on-site; offsetting if shortfall | | Monitoring fee | One-off payment secured in s106, payable before commencement | | Enforcement | LPA enforces s106; responsible body enforces conservation covenants |
Council Monitoring Fees (2025)
Monitoring fees vary by site size and habitat difficulty. Examples from UK councils (February 2025):
| Site Size | Low Difficulty | Moderate | High | | --- | --- | --- | --- | | 0–5 hectares (small) | £2,666 | £3,759 | £4,430 | | 5–20 hectares (medium) | £4,013 | £4,684 | £6,326 | | 20–40 hectares (large) | £6,326 | £7,793 | £8,420 |
Additional 5% if 7 or more habitat types are created.
Development Costs in London
| Service | Cost Range (ex VAT) | | --- | --- | | BNG baseline ecology survey | £1,500–£5,000 | | Biodiversity Gain Plan preparation | £1,000–£3,000 | | HMMP preparation | £1,500–£4,000 | | Annual monitoring visit | £500–£2,000 per visit | | 30-year monitoring (total) | £15,000–£60,000 |
London premium: Expect higher costs due to site complexity, ecology expertise availability, and borough-specific requirements.
When BNG Monitoring Is Required
| Development Type | BNG Required? | | --- | --- | | Major development (>9 houses or >1 ha) | Mandatory since February 2024 | | Small sites (1–9 houses or <1 ha) | Mandatory since April 2024 | | Householder applications | Not typically required | | Permitted development | Check with LPA |
Frequently Asked Questions
Q: When did BNG become mandatory in London?
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) from April 2024.
Q: Who conducts BNG monitoring surveys in London?
A CIEEM-registered ecologist must conduct all BNG surveys. Use the CIEEM Registered Practices Directory to find qualified professionals.
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 target?
The HMMP defines trigger levels and required adaptive management responses. If triggered, remedial action must be taken within agreed timeframes.
Q: Can BNG be achieved on-site in London?
On-site BNG is preferred. The City of London targets 3.0 biodiversity units per hectare on-site. If shortfall exists, off-site gains or statutory credits may be used.
Q: Do I need a monitoring fee for my London development?
Most LPAs charge a one-off monitoring fee secured in the s106 agreement, payable before commencement. Check with your borough council for specific charges.