Well I just got back from a holiday in London , went and got a PCR test within 72 hours and you guessed it, positive! ( I wouldn't have even known I had Covid if it wasn't for the pre departure test)
As I was originally flying in the evening, I didn't want to spend my last day running around getting a RAT test and then if positive trying to re arrange things last minute so getting the PCR test gave me 48 hours to get tickets reissued, accommodation sorted etc without to much stress.
Can confirm I used medispot.co.uk who after 7 days issued me with a certificate of recovery.
Super easy to use, filled in a online form that took 3 minutes , upload your Covid positive test , make payment ( 59 pounds ) and within 24 hours I had a Covid recovery letter saying I was fit to fly.
No problems checking in with it at LHR with the letter ( along side your original positive test ) and away you go.