Green’s Dictionary of Slang

to break wind.

1989		Viz June/July 24: But you can chuff as much as you want.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: chuff 1. v. To pass wind; shoot a bunny rabbit. e.g. ‘Oops! Best open a window vicar. I believe I’ve just chuffed.’.