I'm not sure whether it would be illegal in UK to carry a sign saying "God Hates Fags" in and of itself. Carrying a sign that said "I Hate Fags" might be different. The UK law does not, intrinsically acknowledge "God". However it does (at least superficially) acknowledge peoples right to believe in God so I think it would be interesting to see it tested in a court of law.

Of course, as Erasmus says, there are other laws that could be used. The more recent "anti-terror" laws have been abused in this way to impede free speech and peaceful protest.

John