I'm still waiting for the definition of pornography. Does William Adolphe Bouguereau's A Young Girl Defending Herself Against Eros qualify? How about the work of Spencer Tunick? How about Tennis Girl by Martin Elliott?
Instead of speculating, why don't you look at the British statute books? Wouldn't you expect the same law(s) for print, film and television for instance to apply or at least be a starting point?