I totally agree with New Judge that the appropriate offence, if any, should be Section 5 of the Public Order Act. It was introduced sometime in the mid 1980s? - while I was still a Police Officer - and was seen as the type of offence to help operational Officers deal with ongoing disturbances particularly in public places, as its title suggests.
I made quite a few arrests under S5 myself and it was always very handy, for example, for the yobs gobbing off and swearing in the street, that type of thing.
My only slight reservation in this particular instance is that S5 is overwhelmingly used when an alleged offence is actually in progress, i.e. at the time, and it would be unusual as a rule for it to be brought retrospectively. There are, however, other possible offences which could also be considered - if it comes to that.