I'd definitely agree with the people recommending Robert Rankin.

Tom Sharpe is also funny (Wilt, Porterhouse Blue, etc.)

Also (disclaimer that it's by someone I used to know which may affect my judgement) Go Up by Simon Broadbent is clearly influenced by the Terry Pratchett books set in Ankh Morpork.

I didn't like it quite as much, and it is more middle grade, but A Wizard's Guide to Defensive Baking feels kind of Pratchett influenced.