I know this is old and irrelevant now but my favourite British sitcoms (and some sketch shows), in no particular order, are as follows;

Blackadder
Only Fools and Horses
Red Dwarf
Fawlty Towers
Bottom
The Young Ones
The Office (UK)
Extras
The Inbetweeners
The Fast Show
Little Britain (Series 1 mainly)

Honourable mentions;

Men Behaving Badly
Game On
Absolutely Fabulous
Dad's Army
Morecambe & Wise
The Two Ronnies
Harry Enfield & Chums