The offence of murder could be watered down in the biggest shake-up in decades, under plans by the Law Commission.

The independent body, which makes law reform recommendations to ministers, is launching a consultation about the creation of a US-style system where killers could be tried for either first-degree or second-degree murder, depending on their level of culpability.

It has proposed splitting the crime of murder into two tiers, allowing judges to set a discretionary sentence rather than having to hand out a mandatory life sentence to convicted killers.

The body is consulting about the creation of a new offence of first-degree murder for cases of intentional killing and a lower culpability offence of second-degree murder for cases where the killer intended to cause only serious injury.

The Law Commission also wants jurors to be able to reach a verdict of ‘murder with a partial defence’ when a defendant had the intention to kill but successfully argued a partial defence due to loss of control or diminished responsibility.

It is envisaged that only first-degree murder cases would still carry a mandatory life sentence, with the lower offences carrying a discretionary sentence.

Under the current laws, cases of diminished responsibility are prosecuted as manslaughter rather than murder.

But the Law Commission wants to address public fury over cases like the Nottingham attacker Valdo Calocane who was given a hospital order after admitting manslaughter on the grounds of diminished responsibility following a knife rampage when he fatally stabbed three strangers in June 2023.

The families of victims, Barnaby Webber and Grace O’Malley-Kumar, both 19, were outraged that he was not prosecuted for murder after the CPS decided there was overwhelming evidence Calocane was suffering from a serious mental health condition at the time.

The Law Commission believes that current laws on murder and manslaughter do not accurately reflect a defendant’s intention.

If the recommendations are accepted, it would represent one of the most significant law reforms in generations.

It would mean that in cases involving multiple defendants or gang killings, the prosecution would be able to differentiate between the culpability of a principal offender who delivered the fatal blow and an accessory who assisted or encouraged the principal offender, resulting in ‘more proportionate sentences’, the commission believes.

The consultation will also consider the creation of a ‘bespoke’ homicide offence of controlling or coercive behaviour in an intimate relationship which leads to a victim’s suicide.

It comes after a series of cases where allegedly abusive husbands have been put on trial for murder after being accused of driving their wife to suicide, but juries have been reluctant to convict.

Commissioner for Criminal Law, Professor Penney Lewis said: ‘Homicide offences in England and Wales have never been the object of a coherent and structured reform, and the law has not kept pace with what society now understands about culpability, domestic abuse and the consequences of dangerous conduct.

‘This review offers a timely opportunity to modernise the law and to build a fairer and more proportionate framework that reflects the degrees of culpability of offenders. We want to hear from as many people as possible with experience in this area before we make our final recommendations.’