Used pretty much as "git" (the UK noun rather than the US verb), with roughly the same degree of offensiveness. Maybe there's a dash of "twit" in there too.

Yes, shona, that is much the feeling I got from the contexts in which the term has been used in my hearing. A mixture, I thought of "twit" and "wanker," perhaps?

Incidentally, the term "wank" has been current over here (UK) for quite a long time - I certainly remember using it at school in the '50s - in its masturbatory sense, rather than "wanker" as an epithet; that usage appeared (so far as I'm concerned) in the '60s.