The UK doesn't have a written constitution like the US.
The closest thing we have to the Bill Of Rights is the Human Rights Act, but there is widespread opposition to it based on the fact that it gives rights to prisoners, foreigners and other folks who seem a bit shifty. That enshrines a right to freedom of expression, but provides exceptions "for the protection of health or morals" which I guess would allow this law.
Even in the US, it could be argued that this isn't censorship since you can choose not to be censored (and it could be argued that forcing someone to put their name down on a government list of Men Who Want To Look At Wimmen Nekkid to avoid the censorship is in itself a form of censorship - but that's for the courts to decide and not a random /. commenter)