The Yorkshire Ripper probably committed "many" more attacks on women than the 13 murders and seven attempted murders for which he was jailed, police have concluded.

A secret Home Office report on Peter Sutcliffe and the bungled police attempts to catch him, dating back almost 25 years, was released today under the Freedom of Information legislation. It suggests he not only carried out attacks in Manchester and West Yorkshire but in other parts of the country as well.

Police identified a number of attacks which matched Sutcliffe’s modus operandi and tried to question the killer, who was eventually sent to Broadmoor secure mental hospital, but he was never charged with other crimes.

An inquiry into West Yorkshire police investigation said there was an "unexplained lull" in Sutcliffe’s criminal activities between 1969 - when he first came to the police’s attention - and the first officially-recognised Ripper assault in 1975.

The details came in a report by Sir Lawrence Byford, a former inspector of constabulary, which has been kept under wraps since 1982. Part of the document entitled "Description of suspects, photofits and other assaults" remains censored by the Home Office.

Also partly censored was a section on Sutcliffe’s "immediate associates". Sir Lawrence’s report said: "We feel it is highly improbable that the crimes in respect of which Sutcliffe has been charged and convicted are the only ones attributable to him.

"This feeling is reinforced by examining the details of a number of assaults on women since 1969 which, in some ways, clearly fall into the established pattern of Sutcliffe’s overall modus-operandi."

It added: "I hasten to add that I feel sure that the senior police officers in the areas concerned are also mindful of this possibility but, in order to ensure full account is taken of all the information available, I have arranged for an effective liaison to take place."

The Byford report’s major findings were contained in a summary published by then home secretary William Whitelaw, or have since appeared in books about the infamous murders. But for the first time, precise details of the bungled police investigation have been disclosed.

For example, Sir Lawrence described delays in following up vital tip-offs from Trevor Birdsall, a friend of Sutcliffe’s since 1966. A letter sent to police by Mr Birdsall on November 25, 1980 in which he named Sutcliffe was marked "Priority No 1".

An index card was drawn up on the basis of the letter, and a policewoman found Sutcliffe already had three previous index cards in the incident room records. But "for some inexplicable reason", said the Byford report, the papers remained in a filing tray in the incident room until the murderer’s arrest on January 2 the following year.

Mr Birdsall visited Bradford police station the day after sending the letter to express further misgivings about Sutcliffe. A report compiled on this visit was lost, despite a "comprehensive search" which took place after Sutcliffe’s arrest, said the Mr Byford report.

Sir Lawrence said: "The failure to take advantage of Birdsall’s anonymous letter and his visit to the police station was yet again a stark illustration of the progressive decline in the overall efficiency of the major incident room.

"It resulted in Sutcliffe being at liberty for more than a month when he might conceivably have been in custody.

"Thankfully, there is no reason to think he committed any further murderous assaults within that period."

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