I originally thought the very funny Toast of London would've qualified for this but as it is I'll kick things of with two other woefully ignored series that sank beneath public apathy and lack of critical attention.
Respectable. Shown on C5 in 2006 this features Justin Edwards as an ordinary bloke in a loveless marriage who visits a brothel and strikes up a platonic relationship with prozzie Jodi Albert, mostly dressed in corset and suspenders. What's not to like? Also very droll, esp the Serbian hooker, with attitude.
Plus One. Originally shown on C4 in 2007, this is about a bloke (Daniel Mays) whose ex is getting married to Duncan from 'Blue' (the boy band) and he needs to find someone to take along. Also features ex Eastender Nigel Harman as the brother. Very funny in an Inbetweeners/Peep Show way.
Hung (US import). They made 3 series but I think only the first ever got shown in Blighty. It follows newly homeless, divorced father Thomas Jane who ends up leading a double life as a gigolo. No prizes for getting what the title refers to.
Any others to recommend?