How about The Beiderbecke Trilogy?
Excellent, but not a sitcom. I had a thing for Barbara Flynn then.... (when it was first shown)
Mmmmm. I was totally besotted with Average-size Jill Swinburne... and Dr Rose Marie in A Very Peculiar Practice.
Beiderbecke is definitely not a sitcom though, nor is AVPP. And are they forgotten? I suppose neither of them gets repeated much any more. Both genuine classics though.
Side note about Beiderbecke: the low-speed car chase in the first series goes past two of the houses I lived in as a student. Although I didn't live there until a good few years after it was filmed.
Anyway, if we're broadening the remit of the discussion to comedy-drama serials, how about
Tales Of Sherwood Forest? Starred Pete Postlethwaite as a Nottingham nightclub owner who fantasised about being Rick Blaine in Casablanca. Ran for one series in the late 80s. Then sank without trace. Which is a shame, because I remember it being excellent.