Pepper spray is also illegal in the UK.
> If during that hypothetical protest, there were people jump kicking him and swinging skateboards at him, and he used the pepper spray, would he be charged with battery for bringing the pepper spray in the first place?
Basically, going prepared with any form of weapon in the UK is illegal.
If you picked up something off the street, a piece of 2x4 that was lying around, that sort of thing, then you're likely to be OK if it's clear you were under attack. But if you're packing weapons ahead of time to go out to an event then you should either not go or expect that you will be charged with a criminal offence if you get involved in any trouble.
https://www.cps.gov.uk/legal-guidance/offensive-weapons-kniv...
“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”.