A full review of the law on murder has been demanded by government advisers.

The Law Commission, the government's legal reform adviser, said on Friday that a review is necessary because of the "breadth and depth of discontent" with the present rules.

Currently mandatory life sentences must be issued by judges for offences that are either random, motivated or provoked.

The commission had been asked to consider reforms to the defence of provocation in murder cases.

Its research showed that 64 out of 146 lawyers felt a mandatory life sentence for every murder was "indefensible and should cease".

The commission concluded that flexibility and a grading system for the severity of murder cases should be introduced.

A spokesman said: "A logical system would identify the most serious forms of killing and call them murder, but it might also attempt to identify other forms and grade them for sentencing.

"The information we have had from consultees indicates widespread dissatisfaction with the law from judges downwards, who feel their work is being made difficult by the current law."

No relaxation

But Home Office minister Baroness Scotland said there would be no relaxation of the law.

"Murder is the most serious of crimes and we have no intention of abolishing the mandatory life sentence," she said.

"Where an offender is convicted of murder, the court must pass a life sentence."

She insisted that courts already have flexibility in sentencing through the use of minimum terms.

However the Home Office signalled reforms of the provocation defence will be brought forward in the autumn.

Liberal Democrat home affairs spokesman Mark Oaten said reform would restore confidence in sentencing.

"The current system of life sentences is a mess and the public are fed up of hearing life sentences being given out but not served," he said.

"Whilst the option of a life sentence should always be available, it is wrong for a victim of domestic violence to receive the same sentence as someone who has killed a child.

"If public confidence is to be restored in sentencing then we need a system which is transparent, matches the sentence to the crime, and gives victims the justice they deserve."