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

https://lorenzoobxe263.yousher.com/gatwick-airport-terminal-transfer-shuttle-and-walking-routes-2

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.