For peace of mind, allow at least 2 hours before short-haul flights when departing for Gatwick, and more for long-haul

https://rylanfdkl454.theglensecret.com/gatwick-airport-by-car-best-routes-traffic-tips-and-costs-1

For peace of mind, allow at least 2 hours before short-haul flights when departing for Gatwick, and more for long-haul. Add buffers for rush hour or weekend engineering.