In R v Gnango  UKSC 59 (14 December 2011) Lord Kerr dissented in his orthodox application of the principles of party liability. He held that neither primary liability as principal offender nor secondary liability either as an aider, abettor, counsellor or procurer, or by reason of extended secondary liability (the sort of common enterprise-gone-wrong that in this case all judges agreed to call parasitic accessory liability) applied to the facts.
The facts were simple and are found in the statement of the question of law that arose in this case:
"If (1) D1 and D2 voluntarily engage in fighting each other, each intending to kill or cause grievous bodily harm to the other and each foreseeing that the other has the reciprocal intention, and if (2) D1 mistakenly kills V in the course of the fight, in what circumstances, if any, is D2 guilty of the offence of murdering V?"
So D2 could only be guilty if he was a principal or if he aided, abetted, counselled or procured D1 in the killing of V who was an innocent by-stander. It should be obvious that he was not a principal, as he did not actually commit the murder himself. This was not obvious to Lords Brown and Clarke, and neither but to a lesser extent to Lords Phillips, Judge and Wilson. But they were engaged in extending the law for policy reasons.
The difficulty with orthodox secondary liability was that in this case the jury had not been invited to consider whether there was an agreement that D2 would be shot at, so even if this absurd possibility were a potential basis for liability it was not relevant to this appeal.
D2 could not have aided (etc) D1 in the killing of V unless he had helped (etc) by agreeing to be shot at.
Lord Kerr was correct in orthodox terms to conclude that there was no basis in the circumstances of this appeal to hold D2 liable for the murder of V.
That conclusion was not good enough for the other judges.
Lord Phillips and Lord Judge, with Lord Wilson agreeing, took the extremely pragmatic approach of saying it doesn't matter whether D2 was a principal or a secondary party, he and D1 both acted dangerously in a public place and each should be held accountable for V's death. Either could have killed someone and it was just fortuitous that the person who fired the fatal shot was D1. These judges, and Lord Dyson, preferred the secondary liability route to responsibility but they agreed with Lords Brown and Clarke that principal liability could also be used as the basis for liability.
Nor does the jury have to agree on the basis for liability: it is the conclusion as to guilt that requires agreement, not the route to that conclusion (63).
Well, you can't just pluck someone out of an unruly mob and say this person could easliy have been the one who caused the relevant harm so he should be held responsible for it even if it is known that he didn't actually do it himself. Nor can you pretend that he intentionally assisted or encouraged the commission of an offence when there is no evidence he meant to help or encourage its commission. Yes, the law must further the interests of the community, but there must be a rational, formalist, basis for attributing responsibility for crime. Otherwise we will have a society in which judges can simply say we shouldn't let this person off so we will hold him liable.