As certain characteristics such as intoxication or excitability would be ignored for policy reasons, the defendant's drunkenness was irrelevant. A slow down in traffic (as in being late because of the traffic) is not relevant (Steyn LJ in Acott).

D being drunk, or high with drugs or glue at the relevant time may not be so taken into account, because that, like displaying a lack of ordinary self-control, is excluded as a matter of policy.

A key weakness is that the House intends to leave almost a complete discretion to the jury as to which characteristics should be taken into account. Given recent concerns as to the quality of juries who are sitting in the Crown Court, it might have been desirable for the courts to have developed clear guidance on which characteristics should not be taken into account as a matter of public policy and to have clearly allowed judges to direct juries to this effect.

D, a number of hours after being threatened with a beating the next morning, burnt her husband to death by pouring petrol over him whilst he was asleep.

Held:

D stabbed his wife; she was taken to hospital and put on a life support machine, but suffered two heart failures. After ten days she had suffered irretrievable brain damage and the doctors switched off the machine.

Held: D's act could be regarded as the cause of V's death, and D was convicted of murder. The doctors' decision did not break the chain of causation.

Where the medical treatment given is the best available, there can be little argument about such a principle, but it has been extended to cover treatment which is clearly deficient.

There are obvious policy considerations here: the judges do not want wrongdoers to escape the consequences of their crimes, nor do they want the courts clogged with endless medical debates as to whether the treatment given in a particular case was the best possible.