Sutcliffe confessed to his father John that his mental health had improved

News of review comes as it is revealed he was declared sane 15 years ago

But a report from 2006 has raised questions over other potential crimes

A new review is examining claims that Peter Sutcliffe, the Yorkshire Ripper, may have been responsible for more murders and attempted murders than he was convicted for

Police are investigating claims the Yorkshire Ripper was responsible for a series of murders for which he was never convicted.

Former lorry driver Peter Sutcliffe, 69, was handed 20 life sentences in 1981 for murdering 13 women in Yorkshire, Greater Manchester and Lancashire.

However, the Home Office has said it will review sections of a report by Sir Lawrence Byford, written in 2006, which raises questions over whether Sutcliffe was responsible for a number of unsolved crimes, including murder and attempted murder.

News of a police review comes on the same day the Sunday Mirror revealed Sutcliffe told his father 15 years ago that he had been declared sane - despite being detained at the psychiatric unit at Broadmoor Hosptial in Berkshire since 1984.

Byford's report was partly published nine years ago, but a section linking the Yorkshire Ripper to other potential crimes was censored.

The former chief inspector of constabulary believes claims the Yorkshire Ripper was indeed responsible for more crimes than he was charged with, and over a larger geographic area covering the country.

These included the attempted murders of 20-year-old Leeds University art student Maureen Lea in 1980, whose skull and cheekbone were fractured and her jaw 'completely broken open' by her attacker.

Also thought to be a victim of the Yorkshire Ripper is Tracey Browne, who was repeatedly attacked with a hammer aged 14, in 1975, in West Yorkshire.

In a statement published in the Sunday Times, the Home Office said: 'Should any new lines of inquiry be identified - whether they relate directly to the Ripper case or otherwise - they will be comprehensively pursued.'

Earlier this year, Tim Tate and Chris Clark, a former policeman, made similar claims in their book, Yorkshire Ripper: The Secret Murders.

Mr Tate said: 'We have identified 22 additional murders and eight attempted murders where he is the most likely suspect.

'These now need to be properly investigated.'

Among the unsolved crimes Tate and Clark examined were the brutal murder of Eve Stratford, who was discovered face-down on the floor of her East London home in March 1975.

Her hands were tied behind her back with a stocking and a belt and her blue negligee had been ripped open.

Her throat had been cut so violently with a large knife that her head was almost severed.

Eve was a ‘bunny girl’ hostess at Park Lane’s risqué Playboy Club and had posed nude in Mayfair magazine.

The murders of Eve Stratford, a 'bunny girl' hostess, and Barbara Mayo, a 24-year-old trainee teacher, were never solved and a new police review will now look into whether Peter Sutcliffe was in fact responsible

Scotland Yard initially worked on the theory that she had either met her killer at work or through her glamour modelling work, but failed to make any arrests.

The case came four months before the attack on Anna Rogulskyj in Keighley, West Yorkshire, and another on Olive Smelt in Halifax a few weeks later – cases which became the first officially recorded attempted murders in the gruesome crime catalogue of Britain’s most vicious and feared serial killer, Peter Sutcliffe.

Another potential victim of the Yorkshire Ripper is 16-year-old Lynne Weedon.

She was attacked from behind as she walked home in Hounslow, West London, on September 3, 1975.

Her skull was smashed with one massive blow from a blunt instrument. Her killer removed her blue jeans, leaving her naked from the waist down; he then began sexually molesting her dying body before being disturbed and dumping her body in the grounds of an electricity substation.

Lynne Weedon, 16, was attacked from behind as she walked home in Hounslow, West London, in 1975

Other possible victims include Jacqueline ‘Jackie’ Ansell-Lamb, an 18-year-old legal secretary who was sexually assaulted and battered to the back of her head in March 1970.

The clear cause of death was strangulation with a strand of knotted rope. Revealingly, the killer had posed her dead body.

Crime scene staging is present in just one per cent of homicides and forms a distinctive signature – indeed, it was a hallmark of the Yorkshire Ripper, who frequently killed and mutilated his victims, often face-down.

He then dragged them to their final resting place, where he would typically, though not always, turn them over and arrange their clothing to display their breasts and his frenzied stabbing of the abdomen and groin.

Barbara Mayo, a 24-year-old trainee teacher living with her boyfriend in Shepherd’s Bush, West London, was discovered in woods in Derbyshire, in 1970.

She was face-down, with her clothing in disarray and her jacket spread over her. She had been beaten about the head and strangled with a ligature.

A DNA sample, presumably semen, was found on her clothing –another common part of the Ripper MO.

The near-naked body of Gloria Booth was discovered at 8am on Sunday, June 13, 1971, in brambles on a recreation ground in Ruislip, West London.

She had been viciously attacked. A post-mortem suggested she had been lying face-down for at least half an hour after she was hit over the head, garotted and mutilated.

Tracey Browne, who was repeatedly attacked with a hammer in 1975, is thought to be another victim

Then her body was posed: her bra and blouse had been pushed up to reveal her breasts and she had several nasty-looking wounds to the abdomen – evidence that the crime was far from a ‘typical’ rape.

Sutcliffe used a knotted garotte on his last two ‘official’ victims and was carrying a 3ft length of knotted nylon rope when he was finally caught in January 1981.

The partial removal of Gloria’s clothing was similar to the staging noted in all of the murders for which Sutcliffe was eventually convicted.

The mutilation of her pubic region had a strong parallel with several acknowledged murders. And police discovered distinctive bite marks as found in at least one other murder – made by a man with the same gap in his front teeth as Sutcliffe.

The review may reveal whether Wendy Sewell, Jackie Ansell-Lamb and Gloria Booth were Sutcliffe's victims

Sutcliffe has also been implicated in book, in the brutal 1973 murder of Wendy Sewell.

Innocent Stephen Downing, a 17-year-old cemetery groundsman with learning difficulties, was convicted for the crime and served 27 years.

His case was championed by The Mail on Sunday, and Downing was finally freed by the Court of Appeal in 2002 after his conviction was ruled unsafe.

When Sutcliffe was caught in 1981, he told police about the unusual way in which he killed – details so unusual that it is unlikely such similar crimes could be committed by anyone else.

His MO included prior conversation with his victims, the use of hammer (usually with a round head or ‘ball-peen’) from behind, repeated stabbing after death with a knife or screwdriver, partially stripping and moving his victim’s body and posing them in a ‘staged’ crime scene.

He sometimes used a knotted roped to strangle victims, and semen was sometimes left at the scene.

John Sutcliffe, father of the Yorkshire Ripper, was told 15 years ago during a phone conversation with his son that doctors had declared him as sane

According to Tate and Clark, the officially accepted history of the Ripper’s crimes – the brutal murder of 13 young women and seven attempted murders between 1975 and 1980 – vastly underestimates the true extent of Sutcliffe's crimes.

They claim that out of a total of 78 unsolved murders in the 16 years before Sutcliffe was arrested, the killing of no fewer than 22 women bear the signature of the Yorkshire Ripper, as well as six attacks in which the female victims survived and two attacks on men, one fatal, making a total of 30 unacknowledged Ripper attacks.

They also accuse Sutcliffe of crimes that were not confined to prostitutes or restricted to Yorkshire and the North.

The fresh review into the Yorkshire Ripper comes in the wake of a bid to return Sutcliffe to prison from Broadmoor Hospital, where he has been detained since 1984.

Last month, doctors declared that Sutcliffe was now sane, but according to The Sunday Mirror, this diagnosis was given 15 years ago.

The murderer revealed in a phone call to his father, John Sutcliffe: 'They tell me I am sane now - well that's great.

'But it makes nowt difference. If you asked me what chance I have of ever being released I would say no chance.'

At his trial in 1981, Sutcliffe blamed 'voices from God' for his killing spree.

His father, who died in 2004, reportedly said that his son was a 'nice guy' but mentally ill and had schizophrenia.