As per the existing guidelines, it is possible to fly short-haul with a turnaround and return within one duty period and be exempted from quarantine as long as you don't have a confirmed positive case on board that you have been in contact with for more than 15 minutes. There are also provisions in place for taking rest without entering a foreign country and hence being exempt from quarantine both outbound and inbound. Those normally involve either spending the rest period on the aircraft or being chauffeured to an isolated hotel room and not allowed to leave it until the return flight.
...it's another matter whether any of these guidelines will be needed in the UK soon, maybe except for cargo...