[2] During and after the royal commission there had been several controversial cases, including that of Derek Bentley in 1953 where a 19-year-old defendant was hanged for a murder committed by his 16-year-old co-defendant.

(Bentley's conviction was found to be unsafe by the Court of Appeal in 1998)[3] The hanging of Ruth Ellis in 1955 had also caused considerable unease with the system of capital punishment; Ellis had a strong potential defence of diminished responsibility due to previous, but not immediate, abuse by her victim, but as the law did not provide for such a defence to a charge of murder she was sentenced to death.

[4] In November 1955, after Home Secretary Gwilym Lloyd George announced the government's rejection of some of the Royal Commission's proposals, veteran MP Sydney Silverman introduced a Bill to abolish capital punishment.

Thus, the automatic linkage between the other crime and the murder was broken, and juries were then required to consider more directly whether the accused was culpable when engaging in the conduct resulting in death.

This continuing common law was the basis of the decision in DPP v Smith[8] where the Lords confirmed that neither expressed nor implied malice had been repealed by the section.

In 1953 the Report of the Royal Commission on Capital Punishment[10] took the view that mental abnormality which resulted in a diminished responsibility, was relatively common and potentially of importance to a wide range of offences.

The Commission therefore asserted that a "radical" amendment to the existing law would not be justified for the "limited" purpose of enabling the courts to avoid imposing the death sentence.

Broadly, the difference is that diminished responsibility is characterised by a temporary emotional or mental state which causes the accused to lose control over whether and how to act, whereas insanity is any inherent (internal) defect which so radically affects the defendant that he or she does not understand what is being done or that it is legally wrong to do it (other conditions may cause the accused to become an automaton, i.e. to be unable to control her/his body's movements, see automatism and its case law).

A further distinction is that the defence of diminished responsibility reduces a murder charge to voluntary manslaughter, whereas the defence of insanity excuses the accused of all guilt (but may require the accused to be placed in special care, say, by imposing a hospital order under section 37 of the Mental Health Act 1983, and automatism results in a complete acquittal.

Provocation can be distinguished from diminished responsibility which recognises a reduction in culpability because the defendant does not have the capacity to choose whether to break the law or not.

The defence of provocation was based on the argument that a person who was so provoked as to completely lose their self-control should not be punished in the same way as those who murder wilfully.

The burden is on the accused to prove that she/he: Until the Homicide Act was passed, the mandatory penalty for all adults convicted of murder was death by hanging.

After decades of campaigning, abolitionists secured a partial victory with the Act, which limited the circumstances in which murderers could be executed, requiring mandatory life imprisonment in all other cases.

Five were of people under the age of 18; six of the convictions were reduced either to non-capital murder or manslaughter on appeal, leaving 64 who were liable to be hanged.