Straw had “no rational reason not to free Biggs”

Under measures contained in the Coroner’s and Justice Act, which was given Royal assent last week, Mr Straw could lose the power as early as the new year.

He exercised it this summer when he kept Biggs inside despite a recommendation by the Parole Board that the 80-year-old be released. He later released Biggs on compassionate grounds because of ill health.

The board which considered the case said Great Train Robber Biggs should be let out because he presented no threat to society, but Mr Straw accused him of being “utterly unrepentant” about his crimes.

Parole Board chairman Sir David Latham criticised the decision today, saying their was no “rational reason” to keep Biggs in prison.

He said Mr Straw had been influenced by the feeling that the public wanted Biggs to stay behind bars.

Sir David said: “Jack Straw may well have said ‘My gut feeling is that people do not like the idea of a man who has not admitted he has done something really awful [being released]’.

“I think it was a genuine feeling on his part on the way the public might feel about it, but that doesn’t necessarily mean it was a rational decision.

“I think it’s quite a good example of where politicians find themselves in difficult positions. I do not envy Jack Straw his decision.

“There was in my view no rational reason for it in terms of the way in which the Parole Board has been asked to deal with release...”

He said the public trust in release decisions could be undermined because of the “political element” currently involved.

And he said a legal challenge to Mr Straw’s ruling would probably have been successful.

“I do think the public might well have started to think ‘Is it wise for there to be a political element in the decision-making process because it may distrust the rationality of the decision,” he added.

In his submission to the Ministry of Justice on reforms to the Parole Board’s functions, he called for wide-ranging measures to “depoliticise” early release.

Sir David said the Justice Secretary should also be stripped of his power to decide when prisoners can be moved from closed to open prisons. Such decisions affect when prisoners are likely to be released.

Successive Home Secretaries refused to transfer Moors Murderer Myra Hindley to an open prison before her death in 2002 - despite her pleas.

Sir David said: “We consider there is no proper justification for the present power that we have simply to advise on the transfer of prisoners from closed to open.”

If the proposed changes to the Justice Secretary’s powers were made, it would remove some of the last vestiges of direct political involvement in the release process.

The office still holds the power to issue Royal pardons, but Mr Straw said he wanted to hand it over to judges after he handed a pardon to Liverpool fan Michael Shields in September.

Today, Sir David warned of “overload” in the Parole Board, which faces a backlog of around 2,000 cases, caused, he said, by the introduction of indefinite sentences for public protection (IPP).

To give the Parole Board more independence, its funding should be included within the grant given to the Courts Service, he said.

It should also have the power to compel witnesses and prison officers to attend Parole Board hearings, he said.

A Ministry of Justice spokesman said: “The Justice Secretary made the decision to refuse parole principally because Mr Biggs had shown no remorse for his crimes nor respect for the punishments given to him and because the Parole Board found his propensity to breach trust a very significant factor.

“In the case for compassionate grounds, the Justice Secretary had to consider the medical evidence against well-established criteria.

“The medical evidence clearly showed that Mr Biggs is very ill and that his condition had deteriorated.

“Mr Biggs is subject to the same strict licence conditions as other prisoners on release.

“If he were to breach those conditions or commit any further offence, he would be liable to immediate recall to prison.”