The show employed Ian Martin as a "swearing consultant"; one of his roles is to pen the complex and creative insults used in the show.
Each episode has a credit for "the cast" under the writer credits. This is due to some of the dialogue being improvised.
The only time the BBC vetoed a line of dialogue was this line from Malcolm Tucker following the revelations about Jimmy Savile - "That's inevitable. It's as inevitable as what they'll find in Jimmy Savile's basement after he's dead."