Offhand, LOTSW is the longest-running in terms of timespan from first episode. By episode count it's ChuckleVision, IIRC.
Alf could claim to be the most enduring character, but he spanned at least 4 different sitcoms and a number of his own stand-up esque shows.
(I'm not certain enough of radio sitcoms to include them here.)
60s - Steptoe and Son
70s - Fawlty Towers
80s - Blackadder (except first series)
90s - League of Gentlemen
90s Ab Fab and the 00s has to be The Thick Of It.
I have thought long and hard about this. It was really difficult as there's so many good ones to choose from.
1970s = Dad's Army
1980s = Only Fools and Horses
1990s = Vicar of Dibley
2000s = Coupling
Quote: Aaron @ November 14 2009, 3:06 PM GMTOffhand, LOTSW is the longest-running in terms of timespan from first episode. By episode count it's ChuckleVision, IIRC.
It'll be ChuckleVision from February 2010 for episode count. 
As of the moment:
*Last of the Summer Wine - 289 episodes
*ChuckleVision - 286 episodes
Ah, but ChuckleVision has always maintained its quality.
Quote: Tim Walker @ November 15 2009, 3:04 PM GMTAh, but ChuckleVision has always maintained its quality.
It's ace.
What is Chucklevision?
Quote: AndreaLynne @ November 15 2009, 3:36 PM GMTWhat is Chucklevision?
Here's a sample, featuring Harry Hill.
It's basically a BBC kids shows aimed at god-knows what age range. It celebrates naffness, sometimes deliberately, sometimes accidentally. It's one of those shows which attracts an "adult" audience as well, i.e. layabout students.
Paul and Barry are considered quite safe to be let near children in real life. (And their enemy is the 'Chortles', so nuff said.)
Surely there is no higher accolade?
Quote: Robert D @ November 15 2009, 2:53 PM GMTIt'll be ChuckleVision from February 2010 for episode count.
As of the moment:
*Last of the Summer Wine - 289 episodes
*ChuckleVision - 286 episodes
That's what my list said, yes: but did ChuckleVision not have another series in the last few months?
(You can use BCG tags, BTW.)
I think Fawlty Towers and Father Ted.
And Friends
2 out of 3 ain't bad. 
1970s - Dad's Army
1980s - Only Fools and Horses
1990s - Birds Of A Feather
2000s - The Office
Quote: Terry-K @ November 16 2009, 9:42 PM GMT1990s - Birds Of A Feather
Started in 1989... But aside from that, a brave choice. Kudos to you, sir.