Nighty Night

THE SILENT PARTNER
Yor only prity as you feel

Well it's an old comment so whether you'll see this or not is another matter but I'd recommend 'The Thick of It' even more so with the current state of UK politics this year.

I didn't find The Office depressing at all. Anyway, my favorite depressing sitcoms are Taxi, Mary Tyler, Cheers, and a lot more from the 70s and 80s.

"Steptoe and Son" is arguably the grandfather of bleak Britcoms. "The Thick Of It" could also be very cynical, as could "Drop The Dead Donkey".

Try Game On , it's a sitcom from the 90's about 3 flatmates who are stuck together out of necessity.The first series in particular has some dark themes , here it is on Youtube
https://www.youtube.com/watch?v=CfaVicMbSQw

Well there's
Bottom
that ran during the early to mind nineties. It's essentially about two foul mouthed, unemployed losers who share a flat together in Hammersmith, London. It's humour is more anarchic and lavatorial as as opposed to
The Office
although it does have a depressing premise. It's also more cartoonish and not quite as close to reality with some really O.T.T. Slaptick set pieces and violence. If like me you're a fan of some of the work of Rik Mayall and Adrian Edmondson then you might enjoy it. Just don't expect anything too subtle.
Another fine example is
One Foot in the Grave
, a brilliant sitcom from the mind of David Renwick and starring Richard Wilson and Annette Crosbie. It centres around the curmudgeonly Victor Medrew who lives with his long suffering wife Margaret. Having forced to take early retirement we see him frequently rail against the injustices of the world. It's one of those series that could be hilarious one minute and then seriously dark and poignant. Surprisingly so at times! That aired throughout the nineties as well.
If you want to go further back than that there's
Fawlty Towers
which you'd have to be living in a cave to not at the very least heard of. Airing back in the mid to late seventies and superbly conceived and written by John Cleese and his then wife Connie Booth who both also starred in it, the series centres around the misanthropic Basil Fawlty who with his overbearing wife Sybil run a hotel in Torquay. Although overall not quite as poignant as say
The Office
or
One Foot in the Grave
there are is an air of tragedy that hangs over it even when you can't stop laughing.
Anyway, there's three to get you started with unless you've already seen any of them. There's more I could mention but these are the first three that sprang immediately to mind. Hope I've been of some help.