Ameen Jogee appealed against his conviction for murder. Mr Jogee had taken a man named Mohammed Hirsi to an associate’s home, where both men behaved aggressively and Mr Hirsi stabbed a man. The man died of his wounds and Mr Hirsi was convicted of murder. Prior to the stabbing Mr Jogee had come beside Mr Hirsi in the area where the stabbing took place, with a bottle raised in his hand, and leaned towards the deceased saying he wanted to smash the bottle over the deceased’s head. Mr Jogee was convicted of murder through the doctrine of joint enterprise.
The contemporary doctrine of parasitic accessorial joint enterprise was formulated in Chan Wing Siu v The Queen  AC 168. In Chan Wing-Siu, the Privy Council held that if two people set out to commit an offence (crime A), and in the course of that joint enterprise one of them (D1) commits another offence (crime B), the second person (D2) is guilty as an accessory to crime B if he had foreseen the possibility that D1 might act as she did.
Mr Jogee asked the Supreme Court to review this doctrine and to hold that the court took a wrong turn in Chan Wing-Siu and the cases which followed it. The appellant argued that the Chan Wing-Siu decision is based on a flawed reading of earlier authorities and questionable policy arguments. The respondents disputed those propositions and argued that, even if the Supreme Court were persuaded that the courts took a wrong turn, it should be for the legislature to decide whether to change the existing law, since the law as laid down in Chan Wing-Siu had been in place for 30 years.
The Supreme Court concluded:
the Privy Council laid down a new principle in Chan Wing-Siu when it held that if two people set out to commit an offence (crime A), and in the course of it one of them commits another offence (crime B), the second person is guilty as an accessory to crime B if he foresaw it as a possibility, but did not necessarily intend it. 
The Court described a line of precedent from 1672 up to Chan Wing-Siu that established that for a defendant to be guilty as an accessory she must intend to encourage or assist crime B.
The Court found that the introduction of the foresight principle in Chan Wing-Siu was “based on an incomplete, and in some respects erroneous, reading of the previous case law, coupled with generalised and questionable policy arguments.”
The incomplete, and in some respects erroneous, reading of previous case law
Four cases were cited in Chan Wing-Siu:
- R v Anderson and R v Morris  2 QB 110, which introduced the rule that an “overwhelming supervening event” may “relegate into history matters which would otherwise be looked on as a causative factor.” The Supreme Court in Jogee found that the Court of Criminal Appeal’s decision did not “address the question of what is necessary to establish joint responsibility”, and that Anderson and Morris “provided no foundation for the rule in Chan Wing-Siu.” 
- Davies v Director of Public Prosecutions  AC 378, where the House of Lords opined that if a witness to a stabbing knew that one of his companions was armed with a knife, this would plainly have been evidence on which the witness concerned could be regarded as an accomplice. Therefore, a judge would be correct to give the jury an accomplice warning prior to the witness’ evidence. This opinion was, the Supreme Court held, given “in a very different context and does not provide support for the Chan Wing-Siu ”
- Johns v The Queen  HCA 3, where the High Court of Australia took “an orthodox approach in line with the authorities going back to Collison (1831) 4 Car & P 565”.
- Miller v The Queen (1980) 55 ALJR 23, where the High Court of Australia took “an entirely orthodox approach” to the joint enterprise doctrine.
The generalised and questionable policy arguments
Sir Robin Cooke outlined the Privy Council’s policy considerations in the Chan Wing-Siu judgment:
What public policy requires was rightly identified in the submissions for the Crown. Where a man lends himself to a criminal enterprise knowing that potentially murderous weapons are to be carried, and in the event they in fact are used by his partner with an intent sufficient for murder, he should not escape the consequences by reliance on a nuance of prior assessment, only too likely to have been optimistic.
Lord Hughes and Lord Toulson, in Jogee, said that this outline:
- “may be thought to oversimplify the question of what is the enterprise to which he [D2] has intentionally lent himself”, and
- “implies that he would escape all criminal liability, [whereas] on the facts postulated, if the law remained as set out [then] he would be guilty of homicide in the form of manslaughter…There was no consideration in Chan Wing-Siu of the fundamental policy question whether and why it was necessary and appropriate to reclassify such conduct as murder rather than manslaughter.”
The un-cited cases referred to in the quotation above are R v Smith (Wesley)  1 WLR 1200 and R v Reid (1976) 62 Cr App R 109. As such, the Supreme Court disapproved the Chan Wing-Siu principle and restated the principles that had been established before that case.
The restated principles governing parasitic accessorial liability are:
- The requisite conduct element is that D2 has encouraged or assisted the commission of the original offence by D1.
- With regard to the conduct element, the act of assistance or encouragement may be infinitely varied. Both association and presence are likely to be relevant evidence on the question whether assistance or encouragement was provided, but neither is necessarily proof; it depends on the facts: R v Coney (1882) 8 QBD 534, 540, 558.
- Once encouragement or assistance is proved to have been given, the prosecution does not have to go so far as to prove that it had a positive effect on D1’s conduct or on the outcome: R v Calhaem  QB 808.
- The requisite mental element is intention to assist or encourage the commission of the crime and this requires knowledge of any existing facts necessary for it to be criminal: National Coal Board v Gamble  1 QB 11.
- If the crime requires a particular intent, D2 must intend to assist or encourage D1 to act with such intent.
- With regard to the mental element, the intention to assist or encourage will often be specific to a particular offence. In other cases it may not be. It is enough that the offence committed by D1 is within the range of possible offences which D2 intentionally assisted or encouraged him to commit, such as selling weapons to D1 but not caring how they are then used: Director of Public Prosecutions for Northern Ireland v Maxwell  1 WLR 1350.
- If a person is a party to a violent attack on another, without intent to assist in the causing of death or really serious harm, but D1 escalates the violence which results in death, D2 will not be guilty of murder but guilty of manslaughter (Wesley Smith).
- Where the offence charged does not require mens rea, the only mens rea required of the secondary party is that he intended to encourage or assist the perpetrator to do the prohibited act, with knowledge of any facts and circumstances necessary for it to be a prohibited act: National Coal Board v Gamble.
- Liability as an accessory does not necessarily depend on there being some form of agreement between the defendants.