Just departing LGW we faced a wall of Sussex Police before checking into our flight to CUN - no issues as non-residents but they were turning people around.
I’m in no way condoning rule-breaking, but they said they couldn’t legally turn around non-residents and only issue them with a coronavirus-related infringement penalty, which was only a couple hundred GBP as I understand it.
That being said, not sure they’d have the resources at Gatwick to be so thorough with their checks