This week, his lawyer Saimo Chahal confirmed she will seek to enforce Sutcliffe’s right to be given a minimum tariff – and thus learn when he might be set free. The news provoked huge anger, not least in the North of England where the Ripper struck fear into the lives of millions of women during his five-year reign of terror from the late Seventies.

But new rules brought in five years ago do provide Sutcliffe with a slender legal lifeline to freedom, once the trial judge’s minimum recommended sentence of 30 years is completed. Disturbingly, if he can show he is not a danger to himself or the public, his legal team will say he is entitled to walk free in 2011. They rely on human rights laws and the 2003 Criminal Justice Act.

Police appeal for public help to find the Ripper in 1981

The European Convention on Human Rights lays down key rules. A person’s detention must be lawful and they cannot have a heavier penalty imposed than the one applicable at the time their offence was committed. The laws in Britain changed after an extraordinarily misguided campaign to free child-killer Myra Hindley created a public storm.

Various Home Secretaries were reluctant to free her, fearing a public backlash even after she served 35 years.

A key case before the Law Lords in 2002 changed the guidelines for sentencing some of Britain’s worst killers.

Lawyer Saimo will argue Sutcliffe's case

Previously the Home Secretary himself decreed certain prisoners would never be released. Now only judges would have the power to set a tariff – the minimum period of time a murderer would have to spend behind bars.

The following year the Government brought in the Criminal Justice Act which allowed judges to make whole-life tariffs, to be used in certain exceptional cases. Among those with a whole-life tariff are Black Panther Donald Neilson, Moors Murderer Ian Brady and Rose West. Yesterday, killer Jeremy Bamber was told by a judge that he must spend the rest of his life in jail after he sought a minimum tariff for his sentence.

But a Home Secretary did not set a whole-life tariff for another notorious killer – Beverley Allitt, who murdered four children while a nurse in the paediatric ward of Grantham and Kesteven Hospital.

There are striking similarities between that and Sutcliffe’s case. Under the new law, both Sutcliffe and Allitt are entitled to go to the High Court for an order to determine whether they should serve a whole-life sentence or a defined minimum period after which they could be released, prov-iding they are assessed as risk-free.

Both are in secure hospitals under the Mental Health Act, where they are patients, not prisoners: Sutcliffe in Broadmoor, Allitt in Rampton.

In May 1993 Allitt was given 13 life sentences for a series of offences against children – four murders, three attempted murders and six cases of grievous bodily harm.

And shortly before Christmas last year Allitt’s lawyers achieved the goal Sutcliffe’s legal team have set themselves. They won her case for a minimum tariff. A High Court judge decided against extending the 30-year minimum sentence recommend by the judge at her 1993 trial – even though he believed the Home Secretary would probably have added another 10 years.

Justice Stanley Burnton said the Home Secretary had had the opportunity to extend her sentence before 2002 but had not done so.

He then made a devastating comment: “Since the Home Secretary, having had a lengthy opportunity to do so, did not determine that Ms Allitt should have a whole-life tariff… I find it impossible to arrive at the opinion that he would have been likely to do so. Accordingly, it would not be appropriate to make an order [of a whole-life tariff].”

This legal judgment – made six months ago – will almost certainly be used by Sutcliffe’s legal team. They will argue that the Yorkshire Ripper is in the same legal position as Allitt and deserves confirmation of a minimum tariff. There are disturbing similarities between Allitt and Sutcliffe as criminals. Both are extraordinarily manipulative. Both were transferred out of prison and into a secure hospital, where they enjoyed a more comfortable life. We know this was Sutcliffe’s plan all along after his arrest.

Allitt, within a month of her sen-tencing, was transferred to Rampton because she was “extraordinarily mentally disturbed”. According to a consultant forensic psychiatrist, she had been using self-harm to stay in hospital and out of prison.

But with her minimum tariff confirmed, Allitt must now convince a Mental Health Review Tribunal that she has recovered sufficiently to be sent back to prison – then a parole board will decide whether she is capable of being released on licence. This is the law and if Sutcliffe had a minimum tariff set, he would face the same hurdle.

Allitt clearly gave doctors the impression she did not enjoy harming children. But according to consultant forensic scientist Professor Bob Peckitt, who recently examined her, there was a significant sadistic element to her crimes which had been missed before.

The importance of this is that a murder case involving sadism, under the new law is taken exceptionally seriously by judges if there is more than one victim. These factors are among the start points for a whole-life tariff. But despite there being sadism and four murders, the High Court decided Allitt should have a minimum tariff.

Sexual conduct, substantial pre-meditation or planning, concealment or dismemberment of the body are also additional aggravating factors which allow judges to immediately declare a whole-life tariff. Incredibly, Sutcliffe managed to convince psychiatrists who examined him after his arrest that there was no sexual element to his crimes. He told them he was hearing voices from God.

However, under fierce cross examination from Harry Ognall QC at the Ripper’s trial, psychiatrist Dr Hugo Milne had to concede there could well have been a sexual motive, even though Sutcliffe had assured him there was no sexual element in the attacks. I have long believed Sutcliffe was wily enough to work out that denying he got sexual pleasure from his crimes raised the chances of him being transferred to a mental hospital.

As was said by Harry Ognall at his trial: “If he puts himself forward as a sexual killer, the divine mission [from God] goes out the window.”

Sutcliffe both concealed and tried to dismember the body of Jean Jordan in Manchester in 1977. He hid her body under bushes and returned a week later with a saw and tried to cut off her head to disguise the fact that it was a Ripper murder.

He changed the number plates on his car to avoid capture, sharpened a screwdriver as a murder weapon and switched his killing ground when he realised police surveillance teams were operating. These are all unquestionable evidence of a substantial degree of premeditation or planning.

These facts will certainly be examined during the High Court hearing to determine whether Sutcliffe’s minimum sentence will stand. Because of this I believe his lawyers have an uphill struggle and that Sutcliffe will ultimately fail in his ambition to be freed. Rather, it is more likely – and wholly to be hoped for – that Sutcliffe will end up with a whole-life tariff.

The alternative is too grotesque to contemplate for a public that believes he should never be released and would be political suicide for whichever government allowed it.

The media would be banned from revealing his identity or his whereabouts. This might be acceptable in the case of Maxine Carr – girlfriend of Soham murderer Ian Huntley – but would cause absolute public outrage in the case of Sutcliffe.

There is one final crucial fact that is bound to influence the High Court. When he sentenced Sutcliffe to 20 life terms, with a minimum of 30 years, Mr Justice Boreham said: “That is a long period, an unusually long period in my judgment, but I believe you are an unusually dangerous man. I express my hope that when I have said life imprisonment, it will mean precisely that.”

** Michael Bilton is the author of Wicked Beyond Belief: The Hunt For The Yorkshire Ripper, published by Harper Collins.