For peace of mind, allow at least 2 hours before short-haul flights when departing for Gatwick, and more for long-haul
https://www.mediafire.com/file/wm0hxupi6jetnzu/pdf-30673-98296.pdf/file
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.