For example, you have the word 'piss' in Watership Down, which is rated a U.
Yes, that still surprises me. I don't think they'd get away with it now, and even wonder if they'd edit it out if they showed it in an afternoon slot.
Interestingly, while I was researching all this I came upon a
study* that had been commissioned by the likes of ITC (independent television commission) and the BSC (broadcasting standards commission) to determine the British public's attitude towards swearing in film and tv. If you go to page 52, there's a list of swear words, their perceived severity and ranking. Inevitably the top one is cunt, followed by motherfucker, then fuck. But the ranking of some of the others is a real surprise to me! Twat and 'piss off' are only 13 and 14 respectively, whereas prick is number 7? And wanker is number 4 right below fuck, but shit is way down at 17!
Also interesting is that 'piss' isn't even on there as a single word, independent of phrases like 'piss off' or 'pissed off'.
Baffling...
* The study is from 2000, so may be out of date by now, as we all know that cultural attitudes shift quite rapidly these days...