In an important decision today on 18 February 2015 the Supreme Court handed down its judgment in the case of R v Jogee and Ruddock v R  UKSC 8. The two cases concerned appeals against murder convictions based upon the controversial legal concept of 'joint enterprise' or to give it its less snappy legal name 'parasitic accessorial liability'. The Court was asked to consider the necessary mental element of intent that must be proved when a defendant is accused of being a secondary party to a crime.
The concept of joint enterprise has come under increasing scrutiny and criticism by practitioners and the media in recent years with many calls for its abolition. The concept originated in the Privy Council's judgment Chan Wing-Siu v R  AC 168, and was later reaffirmed by the House of Lords in R v Powell; R v English  1 AC 1.
In simple terms the principle of joint enterprise stated that where an individual (D2) jointly acts with another (D1) in committing crime A, and in doing so foresees a possibility that D1 might commit also commit crime B then D2 could be tried jointly as principal for the second crime if D1 did in fact commit it. For example if a group of youths carried out a street robbery together during which D1 alone stabbed and killed the victim and if D2 knew that D1 carried a knife then it could be shown that D2 foresaw a possibility that D1 might stab someone and therefore he could be convicted of murder despite the fact that he did not in fact hold the necessary mental intent for murder.
The doctrine allowed juries to treat his continued participation in crime A not simply as evidence that he intended to assist crime B, but as automatic authorisation of it. So D2 was guilty under this rule, even if he did not intend to assist crime B at all. In practice this set a lower test for D2 than for D1, who would be guilty of crime B only if he had the necessary mental element for that crime, usually intent. And it is in contrast to the usual rule for secondary parties, which is that the mental element is an intention to assist or encourage the principal to commit the crime.
Critics argued that the doctrine led to a tendency to over-charge accessories to offences and this in turn led to the conviction of a great many defendants for crimes for which they had no intent to commit.
In a unanimous judgment today, the Court held that the law must be set back on the correct footing which stood before Chan Wing-Siu. The mental element for secondary liability is intention to assist or encourage the crime. Sometimes the encouragement or assistance is given to a specific crime, and sometimes to a range of crimes, one of which is committed; either will suffice. Sometimes the encouragement or assistance involves an agreement between the parties, but in other cases it takes the form of more or less spontaneous joining in a criminal enterprise; again, either will suffice. In both cases before the Court the existing convictions for murder were set aside.
The case has been rightly described as a landmark decision and a victory for many who have campaigned against what they saw as the injustice of the existing doctrine of joint enterprise. Understandably there is much media speculation now that this might now open the floodgates for 'hundreds' of appeals. It is important to note that the Court was quick to stress that this correction to the law does not mean that every person convicted in the past as a secondary party, where the law as stated in Chan Wing-Siu was applied, will have suffered an unsafe conviction. A correction to the law does not have this effect. The outcome may in many cases have been the same. Those whose convictions are outside the time limit for appealing would require the exceptional leave of the Court of Appeal, Criminal Division, to challenge them out of time.
It remains to be seen how many appeals will succeed following this ruling but in any event the judgment marks an important correction to the law and undoubtedly this will result in a welcome change to the way in which some of the most serious crimes are prosecuted in the future.