Murder is regarded by the public as a uniquely heinous crime. But murder is not always most foul. Some murders are appalling acts of pre-meditated savagery. Others result from domestic rows, an error of judgment (the victim of a burglary who uses excessive force in his self-defence) or a mercy killing.

As Lord Mustill explained for the House of Lords in a 1997 judgment, the law of homicide is “permeated by anomaly, fiction, misnomer and obsolete reasoning”. The popular understanding of the crime of murder is that it involves the intentional killing of another person. But the legal scope of the offence is much wider. You may be guilty of murder if you commit an unlawful act that kills another human being whether or not you intended to kill, however unexpected the death may be, and even if you positively intended not to kill. It suffices that you had an intention to cause serious physical injury. Most cases of murder involve no intention to kill. Bizarrely, a defendant cannot be convicted of the lesser offence of attempted murder unless the prosecution proves an intention to kill.

Despite the range of crimes covered by the law of murder, the law obstinately insists on one sentence for each such offence: a mandatory sentence of life imprisonment. After the European Court of Human Rights and the law lords criticised the role of the Home Secretary in deciding how long murderers should spend in prison, the Criminal Justice Act 2003 now requires judges to impose a minimum term to be served by a murderer, after which the Parole Board will consider whether to release him (and most murderers are men) on licence.

The mandatory life sentence serves no sensible purpose and should be abolished. As Lord Bingham of Cornhill, then the Lord Chief Justice and now the senior law lord, explained in a lecture in 1998, the sentence conflicts with the basic principle of morality and justice that an offender guilty of a crime should be sentenced by a court to such penalty as the crime merits, having regard to all the circumstances.

For those murderers — and there are some — for whom a life sentence is appropriate, either because of the gravity of the crime or because the offender poses a continuing risk to the public, the judge should retain the discretionary power to impose such a sentence, as with other serious offences. But for other murderers — and there are many — whose offences are less grave and who are unlikely to offend again because their crime was the product of very specific circumstances, a sentence of a defined term is adequate and appropriate. The mandatory life sentence has long been an unjustifiable anachronism. The 2003 Act has emphasised that it is a formula which conceals rather than describes the sentencing reality.

Unfortunately, for reasons that only a political theorist, or perhaps a psychiatrist, could adequately explain, successive Home Secretaries, whether Conservative or Labour, have been reluctant to reform the anomalies of the law of homicide and have insisted on retaining the mandatory life sentence for murder. Home Secretaries present no coherent justification for the current content of the law. They ignore the almost unanimous view of judges and lawyers that reform is needed.

Louis Blom-Cooper and Terence Morris have been studying the crime and punishment of homicide for more than 40 years. With Malice Aforethought (Hart Publishing) is a stimulating contribution to the debate. Not all readers will agree with every aspect of their analysis. Their suggestion that no murderer deserves to remain in prison for the whole of his or her life as appropriate punishment is unpersuasive. Equally unconvincing is their assertion that Myra Hindley did not merit such a punishment for her involvement in the Moors Murders.

But Blom-Cooper and Morris are undoubtedly correct to complain that debate about the law of murder has long been “a dialogue with the political deaf”. Politicians live in fear that any reform of the law of murder and any change in the penalty would lead to them being attacked for “going soft” on a crime the characteristics of which the public do not understand and about which politicians have done little to provide enlightenment. It is a depressing reflection on the poverty of debate on crime and punishment that the Home Secretary, Parliament and so much of the press are unwilling to recognise concepts more sophisticated than thou shalt not kill.