Having done a few 'pan pan's in my time in airliners, we always have to submit a MOR (
CAP 382 refers). Now if you look in the applicability section you will find that only AOC holders have to do this, so I guess (ie. I can't say for sure) you don't have to do anything provided nothing further reportable occurs. If you want to be sure, then give the CAA a quick ring.
Bear in mind that the ATC unit that you transmit the PAN/Mayday call to will have to submit a report, so the CAA will have a record of your distress call. If there is any queries, then they will definitely call you. So I would keep a personal record of what occurs (in some detail in case) but then go down the boozer....
All my opinion of course!