How the Official Gov.uk Metric Calculates Net Gain
The official spreadsheet enforces rigorous ecological multipliers to prevent developers from exaggerating future habitat quality:
1. Temporal Multiplier: Deducts units for habitats that take decades to mature (e.g. broadleaf woodland takes 30+ years, incurring a significant temporal penalty).
2. Difficulty Risk Multiplier: Discounts expected post-development gains based on technical failure risk (e.g. creating species-rich fen has high technical difficulty, reducing claimed unit credit by up to 67%).
3. Off-Site Spatial Multiplier: Penalises off-site units sourced outside the local planning authority boundary (0.75 multiplier if in neighbouring LPA, 0.5 multiplier if outside entirely).
Step-by-Step Procedure:
Confirm ecological baseline was mapped using UKHab classification standards.
Check whether proposed habitats incur high temporal delay penalties (>15 years).
Verify that hedgerow and watercourse units are entered into separate metric sheets.
Ensure baseline date matches the statutory baseline date (30 January 2020 or application date).