I think Porridge is top of my list, it seems to be on "Gold" all the time and I find I can watch it over and over again.
So well written, with great acting from all the cast, even the "minor" characters are good (Groutey and so on).
The way some jokes are "set up" is a masterclass for comedy writers.
I watched the show the other day about when they have the boxing competition and Groutey tries to "nobble" the fights to win on the betting.
Great scene where Fletcher talks to Mackay about a friend of his who was a boxer and he got all "punchy" and finished up an incoherant, non-thinking, vegetable.
"What became of him" asks Mackay.
"He became a prison warder" says Fletcher, "and he is doing very well".