Scores of killers who at present are charged with manslaughter will no longer be able to escape a murder charge under plans outlined yesterday for new categories of first and second- degree murder.

Jealous husbands who kill and plead provocation, or terrorists who plant bombs but give warnings could be convicted of murder, not manslaughter, under the radical shake-up.

Children who kill could be convicted of a new, lower category of crime if it is proved that they are developmentally “immature”.

And violent street robbers who take part in an assault where the victim is killed by another member of the gang will be guilty of manslaughter, not robbery as now.

The proposals, from the Government’s law reform watchdog, the Law Commission, represent the biggest overhaul of the homicide law for 50 years.

The reforms would bring many more killers into the category of murder which at present is reserved for those who intend to kill or cause serious injury.

But women who kill violent and abusive husbands would be able to plead provocation and be convicted of second-degree murder.

The plans, expected to be taken forward by the Home Office, also signal an end to the mandatory life sentence for all murderers. Instead, the judge in a case of second-degree murder would have discretion to impose a shorter sentence.

Professor Jeremy Horder, the law commissioner who led the project, insisted, however, that the proposals would toughen the law.

“In our review we agreed that the law of murder is in a mess. The law can be unclear, unfair, or too generous to killers.”

Juries, he said, also had too few choices between verdicts to reflect how blameworthy the offender really was. If juries brought in a manslaughter verdict, judges were obliged to reflect that in “considerably lower” sentences, he said.

Ending mandatory life for all murderers would change a law dating back to the abolition of the death penalty more than 40 years ago.

Under yesterday’s plans, first-degree murder with the automatic mandatory life sentence is retained for those who intend to kill or do serious harm, as now. But killers who intend to cause serious harm, but not to kill, would be convicted of second-degree murder, not manslaughter as now. The new category of second-degree murder would catch terrorists who plant a bomb or poison supermarket food but give a warning, saying they did not intend to kill. At present they would be convicted of manslaughter as there is no intent to kill.

In 2004-05, 155 killers were convicted of murder and 142 of manslaughter. Professor Horder said: “This is the big change — upgrading some instances of what are manslaughter and calling them second-degree murder, with the expectation that they will be treated with the appropriate degree of sentencing.”

There was a “very big gap” between murder and manslaughter that could not always be met through sentencing, he said.

Victims’ families also “rightly object to the excessive breadth of the different kinds of manslaughter, as compared with the single offence of murder”, he added.

The Home Office is to begin a consultation process next year on how each category should be punished.

Commander Dave Johnson told The World at One programme on BBC Radio 4 that the Association of Chief Police Officers was pleased that some of its concerns had been taken into account but was concerned that criminals may try to reduce murder charges against them from first-degree to second-degree murder by claiming that they were carrying guns “under duress” because of the threat of violence from other gangsters.Rose Dixon, of Support after Murder and Manslaughter, which works with victims’ families, told The World at One: “I would be a little bit a bit concerned over whether some first-degree murders will be downgraded to second-degree . . . some of my members have said to me: ‘Does that mean my loved one is only second-degree dead?’.”

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