S.1 Prevention of Crime Act 1953:
"(1) Any person who without lawful authority or reasonable excuse, the proof whereof shall lie on him in public place any offensive weapon shall be guilty of an offence, and shall be liable-"
Punishable on summary conviction by 3 months imprisonment or level 5 fine; on indictment by 2 years imprisonment and/or maximum fine.
Although there are no express power of arrest for this offence an arrest can be carried out if the general arrest conditions under PACE are satisfied. In any event the constable may seize the weapon in question.
Section 1(4) provides a definition of an offensive weapon:-
'Offensive weapon' means any article made or adapted for use for causing injury to the person, or intended by the person having it worth him for such use by him (or some other person).
Hence weapons become offensive in two ways-
(a) Some weapons are offensive per se because they have been purpose of causing injury or have been so adapted
(b) Any article which has the potential of causing injury is offensive if the possessor has it with the intention of causing injury
The question of whether the article is offensive per se or otherwise has important bearing on the burden of proof:-
If the weapon is offensive per se and it is proved that the defendant had it with him/her in a public place, the burden shifts to the defendant to prove that s/he had lawful authority or reasonable excuse, and the prosecutor is relieved of the burden of proving that the defendant had it with him/her with the intention of causing injury.
(a) Hence for example in the case of spray cans or improvised whips unless the prosecutor can show them to be offensive per se - certainly doubtful in the former case - the s/he would have to show that the sab had the item with him/her with the intention of causing injury.
(a) If the prosecution proves that the article is offensive per se, then the sab would have to prove - on the balance of possibilities - that s/he had a "reasonable excuse" for the possession, and this question of reasonableness is one for the jury.