The home secretary's power to increase the minimum sentence handed down to convicted murderers is "incompatible" with human rights laws, the Law Lords have ruled.

This is the first step towards taking away the powers home secretaries have to extend the length of time murderers must serve before they can apply for parole in England and Wales.

Murderers' cases that could be reviewed:

Dennis Nilsen - killed 15 men Rose West - murdered 10 young women, including her eldest daughter Heather, 16. Arthur Hutchinson - killed a solicitor, his wife and their son and raped their daughter during a burglary Jeremy Bamber - killed his adoptive parents, his step-sister and her six-year-old twin sons

In a test case affecting 225 prisoners, a specially convened panel of seven Law Lords accepted the argument by defence lawyers that judges should be handed back the task of fixing minimum tariffs for prisoners serving life for murder.

Lord Bingham said the power exercised by the home secretary to decide how long sentences should be, was "incompatible" with article six of the European Convention on Human Rights - the right of a convicted person to have a sentence imposed by an independent and impartial tribunal.

But Home Secretary David Blunkett has promised new laws to establish a set of principles which judges will use to fix minimum tariffs in the future.

Killers' case

Home Office Minister Hilary Benn says Parliament must still have a say in the penalties for certain crimes.

"In certain cases, the most heinous crimes, for example, the sexual and sadistic murder of children - life should mean life," he told BBC News 24.

"And we need to make sure that Parliament retains accountability for the framework of sentencing, while recognising that judges will in future hand down sentences for individual cases."

The test case was brought by three convicted killers, including double murderer Anthony Anderson, who was jailed in 1988.

Mr Anderson claimed his human rights have been breached by the increase of his minimum prison sentence to 20 years, after his trial judge had recommended 15.

His success could open the way for appeals by 70 prisoners who have already served the minimum tariff set out by the trial judge, but who are now serving additional time set by the home secretary.

Many prisoners could sue the government.

Whiting: Likely to die in jail

It could also open the way for more than 20 murderers with "whole life" tariffs to have new minimum terms decided by the Lord Chief Justice, Lord Woolf.

Mr Blunkett has insisted that he would not see the most notorious killers, like Harold Shipman, released from prison.

He believes "life means life" and if this judgement goes against him, he will simply change the law.

Brady: Unlikely to ever be released

On Saturday, Mr Blunkett announced that Roy Whiting - convicted of murdering eight-year-old Sarah Payne - should serve a 50-year minimum jail term.

However the House of Lords ruling is unlikely to affect Whiting since his original trial judge, Mr Justice Richard Curtis, said at the time that it was a rare case in which he would recommend a life sentence meaning life.

Staying inside

Rose West was jailed in 1995 for a minimum of 25 years for the "house of horrors" murders of 10 women, but the home secretary later decided on a whole life tariff.

This ruling has no imminent impact on Rose. She has said that she does not want to come out.

Leo Goatley Rose West's solicitor

Her solicitor, Leo Goatley, told BBC News Online: "This ruling has no imminent impact on Rose. She has said that she does not want to come out."

The case comes too late for Moors murder Myra Hindley, who died in prison earlier this month for her part in the killing of five children.

Her partner in crime, Ian Brady, would be an unlikely candidate for appeal.

The judge in Brady's case recommended he serve a whole-life tariff.

Shadow home secretary Oliver Letwin said he thought the current system had been "operating well".

The government's current predicament was as a result of its introduction of human rights legislation, he said.