Is there a law against carrying items with an intent to use them in such a way?
The offence is possession of an offence weapon in a public place contrary s.1 of the Prevention of Crime Act 1953
(1) Any person who without lawful authority or reasonable excuse, the proof whereof shall lie on him, has with him in any public place any offensive weapon shall be guilty of an offence, and shall be liable—
(a) on summary conviction, to imprisonment for a term not exceeding six months or a fine not exceeding £200, or both;
(b) on conviction on indictment, to imprisonment for a term not exceeding four years or a fine not exceeding one hundred pounds, or both.
“offensive weapon” means any article made or adapted for use for causing injury to the person, or intended by the person having it with him for such use by him or by some other person.
There are similar provisions (with subtle differences) in scotland and northern-ireland at s.47 of the Criminal Law (Consolidation) (Scotland) Act 1995 and s.93 of the Justice Act (Northern Ireland) 2011 respectively.