LONDON -- The European Court of Human Rights challenged the British government's attitude to "life" prisoners on Tuesday when it said a political decision to keep a convicted murderer in jail longer than recommended was illegal.

The court in Strasbourg ruled that Britain's Home Secretary (interior minister) had no right to say convicted murderer Dennis Stafford should remain in prison even after the parole board said it was safe to release him.

The judgment -- the second major ruling by the human rights court against the British government in this area -- raises questions about whether politicians, rather than judges, should be allowed to decide how long prisoners spend in jail.

The most notorious of such cases in Britain is that of Myra Hindley -- a sadistic child killer who was jailed more than 35 years ago for the torture and murder of two children. She later confessed to killing two more.

"There was no power under domestic law to impose indefinite detention on him (Stafford) to prevent future non-violent offending," the court said in its judgment of the Stafford case.

"The court concluded therefore that the applicant's detention after July 1, 1997 was not justified." Stafford received a life sentence for a gangland murder in 1967. He was released on licence 12 years later but was jailed again in 1994 for cheque fraud.

The parole board recommended his release in 1997 after serving just half his six-year sentence but then home secretary Jack Straw overruled the recommendation.

Present Home Secretary David Blunkett said he was "disappointed" by Tuesday's ruling but vowed not to let it affect prisoners on "whole life" tariffs, such as Hindley.

"My overarching priority will remain protecting the public from dangerous offenders," he said in a statement.

Legal experts said the European Court judgment puts a serious question mark over government decisions to keep some murderers in jail for the whole of their lives but said that might not help Hindley win her freedom.

"Hindley has no minimum tariff on her sentence," said Mark Littlewood, spokesman for the civil rights group Liberty. "I don't think this will bring her closer to release." Hindley's lawyers have already pledged to take her case to the European Court of Human Rights but declined to make any specific comment on Tuesday.

Hindley and her lover and fellow killer Ian Brady were known as the "moors murderers" because they buried their victims' bodies on bleak saddleworth moor in northern England.

They were jailed for life in 1966 for the murders of Lesley Ann Downey, 10, and Edward Evans, 17. Twenty years after their conviction, they also confessed to killing Pauline Reade, 16, and Keith Bennett, 12.

In March 2000, Hindley's latest bid for freedom was rejected by Britain's highest court, the House of Lords, which ruled that Hindley was "uniquely evil" and said the home secretary had been right that for her, life means life and she should die in jail.

The Strasbourg-based court ruled in 1999 on another British murder case -- the 1993 killing of toddler James Bulger by two 10-year-old boys -- that intervention by then home secretary Michael Howard to impose a minimum sentence on the killers was a violation of their human rights, Reuters said.