Er... It hasn't in the UK. Then again, the British Board of Film Classification didn't have the same issues with nudity, and allowed nudity as early as 1920 (Nude Woman Poses by a Waterfall), for instance. The rules on nudity then tightened for a while, until around 1960, with nudist colony flicks like Naked as Nature Intended. These days, nudity is permitted at all classification levels (including U and PG) provided the context is not sexual. If it is, then a higher classification is applied.