" If a person is a party to a violent attack on another, without an intent to assist in the causing of death or really serious harm, but the violence escalates and results in death, he will be not guilty of murder but guilty of manslaughter. So also if he participates by encouragement or assistance in any other unlawful act which all sober and reasonable people would realise carried the risk of some harm (not necessarily serious) to another, and death in fact results: R v Church [1965] 1 QB 59, approved in Director of Public Prosecutions v Newbury [1977] AC 500 and very recently re-affirmed in R v F (J) & E (N) [2015] EWCA Crim 351; [2015] 2 Cr App R 5. The test is objective. As the Court of Appeal held in Reid, if a person goes out with armed companions to cause harm to another, any reasonable person would recognise that there is not only a risk of harm, but a risk of the violence escalating to the point at which serious harm or death may result. Cases in which D2 intends some harm falling short of grievous bodily harm are a fortiori, but manslaughter is not limited to these." para 96.
"The effect of putting the law right is not to render invalid all convictions which were arrived at over many years by faithfully applying the law as laid down in Chan Wing-Siu and in Powell and English. The error identified, of equating foresight with intent to assist rather than treating the first as evidence of the second, is important as a matter of legal principle, but it does not follow that it will have been important on the facts to the outcome of the trial or to the safety of the conviction. para 100"
"We regard that submission as hopeless. The jurys verdict means that it was sure, at the very least, that the appellant knew that Hirsi had the knife and appreciated that he might use it to cause really serious harm. In returning to the house, after 2.00 am, in the circumstances which we have summarised, the appellant and Hirsi were clearly intent on some form of violent confrontation. The appellant was brandishing a bottle, striking the car and shouting encouragement to his co-defendant at the scene. There was a case fit to go to the jury that he had the mens rea for murder. At a minimum, he was party to a violent adventure carrying the plain objective risk of some harm to a person and which resulted in death; he was therefore guilty of manslaughter at least. The choice of disposal is whether to quash the appellants conviction for murder and order a re-trial or whether to quash his conviction for murder and substitute a conviction for manslaughter. We invite the parties written submissions on that question." para 107
