In case 1, P, D and X went to a drug dealers home for the joint criminal venture of buying cannabis but during the course of the JCV, P and D realised that X had a gun and contemplated that he might kill the rug dealer. They nevertheless continued in the JCV and when X did kill the dealer, they were convicted as accessories to the offence. HL dismissed their appeals on the grounds that where one party, in the course of the JCV, foresees what the other party might do, he can be convicted as an accessory on that basis (Lord Hutton).
In case 2, E and X had attacked a policeman, V, with wooden sticks. X pulled out a knife (which E was not aware that X had) and X inflicted fatal wounds. HL quashed E’s murder conviction since X was operating outside the scope of the JCV, as demonstrated by the use of a weapon whose presence was unbeknown to E. However, Lord Hutton says that if the principal uses a weapon that is as dangerous or less dangerous than the one which the accessory contemplates the principal using (e.g. I stab someone when my accessory thought I would shoot them) there is no escaping liability. It is only when the principal uses a more dangerous weapon than the one that the accessory envisioned that he has moved beyond scope of JCV.
A problem was raised: The principal had to intend death to be convicted of murder, whereas the accessory only had to foresee possibility of another killing a person to be convicted of murder. I.e. the accessory can be guilty of murder by a lesser mens rea than principal and in fact is being convicted of murder by recklessness. Lord Steyn (and other judges) say it is thus for policy reasons so as to afford public protection against people operating in gangs + proof of intent on the part of the accessory would be impossible. Lord Hutton said that Majewski established that policy was a consideration: not just pure logic.