The Upper Hand. (kind of)
Portrayal of cohabitation in sitcoms Page 2
Dad's Army is an interesting example with Wilson and Mrs Pike.
There's the episode 'Bells' from Blackadder 2.
I'd love to post a list of ones I'm looking at, only I'm actually just about a quarter of the way through all the lists of British TV sitcoms I can find, creating a basic pile of ones that look interesting from this angle, and planning to then revisit each in detail. I'll have something more concrete in a day or two, so as you say it might be a better idea for me to get that sorted and then ask if anyone can add to it or comment on its contents, rather than have people racking their brains for things I've already got on my list.
Thanks for all leads so far - I'll be chasing each one up.
If you want creepy, then there's David and his mother in Psychoville.
Or what about Rod, Jane and Freddy?
Quote: Afinkawan @ June 7 2010, 3:15 PM BSTIf you want creepy, then there's David and his mother in Psychoville.
Or indeed Tubbs and Edward in League of Gentlemen. 
How Not To Live Your Life.
The Last Salute has some element of cohabitation, although much like Dad's Army and Clarence, it was made in the 1990s and set in the 1950s.
Quote: Tomtom08 @ June 7 2010, 2:30 PM BSTWhat we're more interested in is the explicitly sexual non-marital cohabitation situations.
Porridge
How Not To Live Your Life looks interesting, but I'll probably park it for a while as it's so contemporary that it assumes that cohabitation is not at all an edgy, alternative lifestyle. I hadn't even heard of The Last Salute (!) - ta for the lead.
Some info on it here: https://www.comedy.co.uk/tv/the_last_salute/
Quote: Kevin Murphy @ June 7 2010, 4:06 PM BSTPorridge
Well Samson and Delilah were minor characters. But seriously Going Straight where Godber has moved in with Imogen fits the bill - with Fletcher as a rather disapproving Dad.
Whatever Happened To The Likely Lads is an interesting counterpoint with Bob and Thelma not co-habitating before marriage, despite already having bought a home together.
Thanks for the above. I suspected there might have been a thread in GS about Godber living with Fletch's daughter, but couldn't find a specific reference (plot summaries will often skim over details like this, naturally) - I'll hunt down those episodes, as it sounds just the kind of incidental portrayal of cohabitation and dis/approval that we're looking to trace. WHTTLL is as you say a good counterpoint - "Compare and contrast changing attitudes to cohabitation amongst engaged couples in WHTTLL and As Time Goes By (50 minutes, no talking or chewing gum)".
I think Clarence (1988) with Ronnie Barker had him and Josephine Tewson cohabiting towards the end, rather than getting married. And didn't Robin's Nest have the main couple living together unmarried?
Quote: Badge @ June 7 2010, 3:07 PM BSTDad's Army is an interesting example with Wilson and Mrs Pike.
I keep thinking that more and more after watching it all these years. It s seems TV was very complicit in persuading us the modern Tory tabloid line that sex was only invented in the 60s when the reality was that people were a lot more liberal about people's personal lives before then as long as you kept it discreet.
Dad's Army seems to capture this brilliantly, everyone knows what is going on and even Mainwaring vary rarely wags his finger. Same can be said of the gay vicar.