Hi Tony
We would then look at Case Law for guidance
(example)
Whilst three or more persons must have been present and used or threatened unlawful violence, it is not necessary that three or more persons should actually be charged and prosecuted: (R v Mahroof (1988) 88 Cr App R 317) (R v Fleming & Robinson (1989) 153 JP 517). The charge must make clear, however, that the defendant was one of the three or more involved in the commission of the offence.
The expression "present together" does not require any degree of co-operation between those who are using or threatening violence; all that is required is that they be present in the same place at the same time, R v NW, CA, 3 March 2010.