By Peter Gould BBC News Online

Ironically the Law Lords' ruling came too late for Moors murderer Myra Hindley, who died two weeks ago as she waited to hear the outcome of the case.

The issue will now go to Parliament but the government believes there has to be a way of ensuring some of Britain's most dangerous prisoners are never released.

The test case was brought by lawyers acting for double murderer Anthony Anderson, who had his minimum sentence increased from 15 to 20 years by the home secretary.

Retribution

The ruling has been eagerly awaited by many other convicted murderers who hope to see their sentences cut.

Rosemary West has a "whole life" tariff

In all, 225 prisoners are thought to have had their "tariff" set by the home secretary.

This is the term for the minimum length of time a prisoner is supposed to serve to satisfy the demands for "retribution and deterrence".

Only when this punishment phase is completed can the prisoner be considered for parole in the light of their rehabilitation and any possible threat they might pose to the public.

Until now, the process of fixing a tariff has taken place largely out of the public eye, which is one of the reasons the system has come under fire.

When a murderer is found guilty, he or she is automatically sentenced to life imprisonment. On average, that means around 15 years behind bars.

Heinous

The trial judge may try to ensure the prisoner does not get out too soon by recommending a minimum sentence to be served.

David Blunkett: "Some killers should die in jail"

It could be 20, 25, or even 30 years.

The Lord Chief Justice reviews the decision, and either endorses the recommendation or amends the figure.

But the home secretary of the day, be he Labour or Tory, has often decided to impose his own tariff.

For some prisoners, convicted of the most heinous crimes, the minimum sentence has been increased substantially.

This is what happened in the case of Hindley. Successive home secretaries raised her tariff until she joined a small group of prisoners given a "whole life" tariff.

The intention was she would end her days in prison, and when she died earlier this month, she had spent 36 years behind bars.

Secrecy

In the case before the Law Lords, lawyers argued it was wrong for the home secretary - a politician - to interfere in the judicial process.

Dennis Nilsen: Could he really be free in 2008?

Considering a sentence in secret was a denial of the prisoner's right to a fair hearing in public, it was argued.

A politician, unlike a judge, might well be swayed by public opinion, rather than considering the facts of the case dispassionately.

Hindley's supporters said this was exactly what happened to her. No home secretary wanted to risk the wrath of the newspapers and voters by allowing her to go free.

Of the 225 prisoners whose tariff has been set by the home secretary, about 70 are thought to have served more than the minimum period recommended by judges.

Attention will be focused on the group of 22 prisoners believed to be serving "whole life" tariffs.

Among them is the serial killer Dennis Nilsen, convicted of the murder of six young men in 1983.

In his case, the original recommendation is thought to have been 25 years. If that now becomes his tariff, he could in theory be eligible for parole as early as 2008.

Notorious

Others told after their trials that they would never be released include the House of Horrors killer Rosemary West and Railway Rapists John Duffy and David Mulcahy.

Myra Hindley did not live to hear the ruling

The Law Lords have now ruled that the home secretary's power to set a tariff is not compatible with the European Convention on Human Rights, which says a convicted person should have their sentence set by an independent and impartial tribunal.

But while politicians will now be excluded from this process, it will not mean an end to the practice of setting tariffs.

The Home Secretary, David Blunkett, intends to bring legislation before parliament to establish a "clear set of principles" under which judges in England and Wales will set minimum sentences.

In Scotland and Northern Ireland, tariffs are already set by the judiciary.

The new legislation will probably mean that prisoners who have had a tariff extended by the Home Secretary will have their cases reviewed by a judge.

But Mr Blunkett has made it clear that for some crimes - such as the sexual or sadistic murder of children - a life sentence should mean life.