If it is illegal here in the UK, then I'm breaking the law. Although I have never heard of someone getting arrested having a fetish for Japanese cartoons fucking each other senseless.
If it is enforced though, it'd probably only get enforced where Loli images are concerned, and it'd be used as evidence towards owning Child Pornography. You know how close-minded Brits can be when it comes to Paedophilia. Something like that can ruin you for life even if proven innocent. Whether Loli actually
is classed as CP here in the UK is another thing entirely though.
Edit:
Found something about Loli
Wikipedia wrote...
Prior to this, although not explicitly in the statutes,
the law has been interpreted to apply to cartoon images, though only where the images are realistic and indistinguishable from photographs. The new law however covers images whether or not they are realistic.
Reference
Basically confirming what Age said, the law on what is legal and what isn't is incredibly vague.
Edit-Edit:
From a quick search on Google, I've found nothing mentioning laws of Cartoon pornography in the UK except on Wikipedia and Yahoo Answers! (Fuckin' joy) But from what little I've found, all "Legal" hentai in the UK has to have characters depicted as 18 or over. Funny that, seeing as the legal age here for sexual consent is 16. Anyway by the looks of things, Loli's illegal and DFC is barely legal. I'm guessing the schoolgirl tag is illegal as well, unless it's an 18+ high school if such a thing exists in Japan.