This thread has got me remembering some brilliant British comedy series - none of them are sketch shows or adaptations of comic books (Porterhouse Blue!) , but I'm not sure they all fit with the label 'sitcom'
Black Books
Auf Wiedersehen, Pet
Brass
Green Wing
The League Of Gentlemen
Coupling
Extras
Two Pints Of Lager And A Packet Of Crisps
Steptoe And Son
Rising Damp
A Touch Of Cloth
Men Bahaving Badly
No Offence
The New Statesman
I would put all of them above The Vicar of Dibley and Only Fools And Horses. But then I'd put Chelmsford 123 with its wobbly sets, lack of a script and half-arsed acting above those two.