I read somewhere that the people making Frasier wouldn't allow Ms Leeves to use the Manchester accent she's perfectly good at producing, because they didn't think Americans wouldn't understand it or something. So they insisted she made up another one which bears no resemblance to anything anybody in Manchester ever spoke.

But the most grotesque ones are probably some of the Oirish accents they've throw at us from Hollywood over the years. Which is puzzling, because I'd have thought there'd have been plenty of people to put them right right on that.