The one major thing that the BBC seems to have forgotten is that sitcoms work best when played by professional actors (not stand-up comedians or TV presenters).
Harry H Corbett, Wilfred Brambell, David Jason, Nicholas Lyndhurst, Arthur Lowe, John Le Mesurier, Richard Wilson, Annette Crosbie, Patricia Routledge, Clive Swift, etc all were/are extremely talented actors, so it's unsurprising that when presented with great scripts (by professional scriptwriters) they turned in some superb performances.
However there currently seems to be an obsession at the BBC with getting stand-up comedians to try to write sitcoms and then, even worse, to star in them. (I recognise that the sitcom referred to in the question above doesn't quite fall into that category but it's very much the same approach from the BBC).
The BBC has a superb scriptwriter (of both sitcoms and sketch comedy) already working for them on Radio 4. (John Finnemore). If they allowed him to write for TV, and filled the roles with professional actors, they'd almost certainly have a hit on their hands.