Most local libraries contain straightforward law books which would help you identify whether something is against the law or not. You don't say whether you are concerned about a criminal matter or not, but you can only be arrested for certain types of offences, and if you are arrested, the police should tell you what for and why (Police and Criminal Evidence Act, 1984). You could also try looking at www.hmso.gov.uk, which lists all UK legislation since 1988. Failing that, write to your MP!