I was on the jury in a GBH trial several years back where the judge had to go into a long spiel on where the law stood with this. One guy on trial, several others had vanished after the act - never charged. A group of lads brutally attacked 2 men and 2 women outside a nightclub. The injuries were nasty, but it couldn't be proved who did what exactly.
The legal precept of joint enterprise meant that the defendant was legally guilty - whether he was the one who did this kick, or that punch etc. He admitted taking part in the act and offered only his defence that he was now working with disable children
I remember the jury had HUGE problems with this. Everyone agreed he was there. He admitted he was there. The judge's instruction therefore implied he was guilty via joint enterprise, though noone could state for definite what he had done exactly. He got 18 months.