Researchers present a percentile-based calibration of the Canadian Forest Fire Weather Index (FWI) System for the United Kingdom (UK), developed from numerical weather prediction data, and evaluate it using historic wildfire records. The Fine Fuel Moisture Code, Initial Spread Index and final FWI component of the FWI system show the greatest predictive skill for UK wildfires. The findings provide useful insights for any future redevelopment of the current operational UK fire danger rating system.