David Blunkett's former lover kept a detailed personal diary of their affair and is considering turning it into a book, it was reported today.

Kimberly Quinn has "potentially devastating" recollections of their three-year relationship in handwritten form and on computer files, her friends told the Evening Standard.

Mrs Quinn, 44, is being urged by friends to use these as the basis of a book which would give her side of the story, once her legal battle with the former Home Secretary over access to her two-year-old son William is resolved.

Mr Blunkett, 57, is pursuing legal moves to gain access rights to the boy, whom he says is his son. He resigned as Home Secretary last week after Home Office e-mails linked him to the fast-tracking of a visa for Mrs Quinn's nanny. His political future hangs in the balance after Sir Alan Budd's report into the so-called nannygate affair failed to exonerate him entirely.

Claims of the existence of a diary are being seen as Mrs Quinn's revenge, after sources close to Mr Blunkett were suspected of revealing that she had also had an adulterous affair with Simon Hoggart, the Guardian sketch writer .

A friend of Mrs Quinn told the Evening Standard: "Kimberly will never want to be seen as a 'kiss and tell' merchant. To an extent the fact that she is even contemplating the idea of a book is another warning shot to Blunkett." Literary agents are said to have estimated that the memoirs could be sold for up to £1.5 million.

The revelations came as Michael Howard called for a fresh inquiry into the affair of the visa application. The Tory leader said the Budd inquiry, which reported yesterday, left too many questions unanswered. The affair also raised wider questions about how government was conducted, he added.

In his report, Sir Alan found that "a chain of events" linked Mr Blunkett to the speeding up of the visa application, but was unable to discover whether Mr Blunkett had issued specific instructions for Leoncia Casalme’s case to be fast-tracked, or if he had merely used her case as an example to complain about backlogs at the Immigration and Nationality Directorate.

Speaking on the BBC Radio 4 Today programme, Mr Howard said: "The worry has to do with the way Government is conducted. What we have seen here is again what we saw in the Butler inquiry when minutes weren’t kept, faxes are lost, telephone calls take place and no record is made of them, meetings take place and no record is made of the meeting. There are serious questions here about the basic integrity of the way in which Government is carried out."

On the same programme, John Prescott, the Deputy Prime Minister, conceded that Mr Blunkett had "made a mistake" - appearing to contradict Tony Blair who said that Mr Blunkett left office with his integrity intact - but insisted that he had already paid the "final" price by resigning.

He said: "He admitted that he had a conflict in the personal handling of this case. It was contrary to the rules of ministers... He has been found guilty of the offence, basically, that’s what happened. But at the end of the day he has faced up to his full responsibility and resigned. That’s the most a minister can do."

Mr Prescott, who accused Mr Blunkett of arrogance over his criticisms of fellow Cabinet ministers, added: "He’s a very capable minister, a very able minister. He’s made a mistake here, there’s no doubt about it, but an awful lot of people benefited from the measures he brought in... He did have a major influence on politics."

Whitehall's standards watchdog said serious questions remain unanswered by the inquiry. Sir Alistair Graham, chairman of the committee on standards in public life, said the Budd report had not revealed if there was a breach of either the ministerial code or the civil service code.

He said: "All of these recent and unfortunate events reaffirm the need for a Civil Service Act to put the core values of the civil service - to act with integrity, propriety and impartiality, and to select on merit - on a statutory footing subject to parliamentary scrutiny.

"I continue to believe that this is the most effective way of delivering necessary public and parliamentary confidence." The committee is to meet in January to see what lessons could be learned from the inquiry.

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