Red Faction said:<goes to check what the law is on carrying knives is>
In short: You can´t carry a knife or anything else "for your own protection" as it would be an intended offensive weapon, (s.1 Prevention of Crimes Act 1953) - arrestable and I think a two year imprisonment sentence.
Any "made" (i.e. flick knife, lock-knife, combat knife, cosh, baton, knuckleduster, martial arts weapon) or "adapted" (e.g. sharpened comb, broken bottle) offensive weapon would be an offence REGARDLESS of your intent.
Any sharply pointed or bladed implement at all (except a free-folding pocket knife with a cutting edge of less than 3") is an offence under s.139 Criminal Justice Act 1988, again regardless of intent.
In all cases there are defences of lawful authority or reasonable excuse. The latter could be given a run if you are in specific, genuine, provable fear at a particular time / place ... but I wouldn´t be popping down to Ladbrokes to put a few bob on it succeeding!
