GTAIV didn't just pass classification muster in Britain, it passed completely uncut. In clearing the game for release, though, the BBFC had to look at (then detail) everything the game had to offer, from the palatable stuff like just driving a car around a virtual city to the less palatable stuff. Like this:
During gameplay the character can pick up prostitutes... What follows is an un-detailed portrayal of masturbation, fellatio and intercourse. The character can also visit lap dancing clubs and request a private dance.
Saucy. Those staunchly in the anti-nipple-and-dangly-bits camp need not worry, though, because "while the game contains sexualised dancing and the portrayal of sex, there is no sexualised nudity". You can read more of the leaked BBFC report at the link below.
BBFC: GTA 4 to feature masturbation and intercourse [videogamer]