The Public Order Act requires the use or threat of violence such that a notional person of reasonable firmness would be in fear for their safety.
Thereafter it's mostly about numbers: 12 or more for Riot; 3 for Violent Disorder; otherwise Affray.
Riot also needs a 'Common Purpose'.
Anyone charged will likely be for Violent Disorder. Easier to prove.
A relative of mine was literally* 'read the Riot Act', failed to comply and was transported to Australia.
* and I mean literally in the sense of literally, rather than the now more common, literally in the sense of figuratively