What Is a BNG Monitoring Survey?
A BNG (Biodiversity Net Gain) monitoring survey is required to verify that biodiversity gains promised in a planning application are being delivered and maintained over time. Under England's Environment Act 2021, most developments must achieve a minimum 10% biodiversity gain, secured for 30 years through a Section 106 agreement.
The monitoring checks that:
- Habitats created or enhanced are present and of correct area
- Habitat condition meets target standards
- The biodiversity gain is being maintained as committed
Monitoring Schedule
Typical monitoring occurs at: Years 1, 2, 3, 4, 5, then every 5 years to 30 years (some councils use Years 1, 3, 5, 10, 15, 20, 25, 30).
Costs (Harrow/London 2025)
| Cost Type | Range (ex VAT) | | --- | --- | | Ecologist per survey | £1,000–£5,000 per monitoring visit | | 30-year total (basic 5ha site) | £20,000–£25,000+ | | Council monitoring fee (small 0–5ha, low difficulty) | £2,470–£2,666 (one-off at S106 signing) | | Council monitoring fee (medium 5–20ha, high difficulty) | £6,728–£10,821 | | Initial BNG assessment (small sites) | From £950 |
Council fees cover: report review, site visits, travel, administration, and enforcement support.
Deliverables
- UKHab survey — baseline biodiversity assessment using DEFRA Statutory BNG Metric
- Habitat Condition Assessment — scored condition of each habitat type
- QGIS habitat mapping — existing and proposed habitat maps
- BNG metric calculations — existing vs. proposed biodiversity units
- Habitat Management and Monitoring Plan (HMMP) — 30-year management strategy
- Monitoring reports — submitted to landowner, Harrow Council (LPA), and Natural England
Harrow Coverage
BNG applies across the entire London Borough of Harrow. Key habitats in the area include:
- Ancient woodland (Harrow Weald, Stanmore Common)
- Bentley Priory Nature Reserve
- Ponds and lakes, hedgerows, amenity grassland
- National Character Area: Northern Thames Basin
Frequently Asked Questions
Q: Does my Harrow development need BNG monitoring?
Minimum10% BNG is mandatory for most developments under the Environment Act 2021. Small-site exemptions apply — check with Harrow planning department.
Q: How long does BNG monitoring continue?
BNG is secured for 30 years through a Section 106 agreement. Monitoring reports are typically required at Years 1, 2, 3, 4, 5, then every 5 years.
Q: What is the DEFRA Statutory BNG Metric?
The DEFRA Statutory BNG Metric calculates biodiversity units for habitats before and after development, using habitat area, condition, and distinctiveness to determine whether the10% gain target is met.