Mr Blunkett’s attempt to establish the paternity of the child born two years ago to his former lover, Kimberly Quinn, was nearing its conclusion at that moment.

Mrs Quinn, 44, who is expecting her second child in February and has been signed off work until May because of acute stress, is resisting pressure to force her into another DNA test.

Mrs Quinn argued that the DNA test should be postponed until after she has given birth to her child. A provisional DNA test, which is not legally binding, has indicated that William is Mr Blunkett’s child.

It was Mr Blunkett’s determination to force the issue which prompted an angry and distressed Mrs Quinn to leak to a Sunday newspaper a spate of damaging allegations about the Home Secretary’s alleged involvement in her nanny’s visa application.

The Times has also established that in order to establish that he is William’s father, Mr Blunkett is likely to have had to specify every time that he had sexual relations with his former mistress.

Mrs Quinn’s husband Stephen, 60, the publisher of Vogue, is said to be shattered by the extent of his wife’s betrayal with Mr Blunkett over the course of the three-year affair. He is said to now have been made aware of the exact times and places of Mr Blunkett’s trysts with his wife, which has forced him to conclude that the unborn child is probably the Home Secretary’s.

Mr and Mrs Quinn believe that the second child was probably conceived when she was on a week’s holiday in Corfu with the Home Secretary and her son at the end of May.

Mr Quinn has vowed to his friends that whatever the outcome of the DNA test on William, and subsequent test on the unborn child, he will carry on as if he is their natural father. In a rare public comment, speaking outside his Mayfair home yesterday, he made clear that he was staying loyal to his wife: “I love my wife. I love my family. I would do anything to look after them.”

Mrs Quinn, who has been married before, was desperate for a child when she married Mr Quinn in 2001. When she began her affair with Mr Blunkett in the same year, she feared that time was running out to have a child. One of the couple’s closest friends said: “Kimberly and Stephen had experimented with a form of artificial insemination. He had no reason to doubt that William was his child.

“He knew nothing about any of this until it was leaked to the News of the World in August. But he has remained re- markably stoical despite everything.”

The friend added: “He is desperately worred about the effect this is having on Kimberly and the unborn baby. He will stick with her and his family. Ironically, the Home Secretary’s pressure is bringing them closer together.” But even Mrs Quinn’s best friends have questioned the wisdom of her decision to make so many damaging allegations about Mr Blunkett to a Sunday newspaper.

One friend said: “If, as it seems, he is the father of her children both Kimberly and Stephen have to be realistic. Blunkett will be entitled to visiting rights and it seems he will exercise those visiting rights. To start a war with the Home Secretary seems reckless.”

They privately accuse Mr Blunkett of hypocrisy in his stance over the child. As Education Secretary in July 2000 he issued guidelines to schools which stated: “Within the context of talking about relationships, children should be taught about the nature of marriage and its importance for family life and for the bringing-up of children.”

The friend said: “What’s his view on Kimberly and Stephen’s family?”

Mrs Quinn, the publisher of The Spectator magazine, was yesterday at her home in Mayfair after triggering the political furore over her weekend revelations.

The daughter of a wealthy Californian family, she met Mr Quinn when she went to work for the publishing house Condé Nast in the 1990s when he was publishing director of GQ magazine. At the time, she was married to Michael Fortier, an American banker. Mr Fortier has accused Mr Quinn of beginning an affair with his wife while they were still married.

Mr Quinn, was born in County Kilkenny to a traditional, solid, Irish middle-class family. He came to Britain in the late 1960s to find work.

Mr Quinn, who did not attend university, rose effortlessly through the ranks of the publishing world. He increased sales on magazines as varied as Business and Harpers & Queen. In the 1980s he launched GQ, one of the first lifestyle magazines aimed solely at men.

Linda Kelsey, the former editor of Cosmopolitan and She, knew Mr Quinn when he was a publisher at the National Magazine Company. Ms Kelsey said: “He was charming, witty and hard-working, and someone who liked to enjoy himself.”

Nicholas Coleridge, the managing director of Condé Naste, made Mr Quinn the publisher of Vogue. In October he was promoted to the new position of Condé Nast’s senior publishing director.

Mr Quinn used to be best known in the publishing world for his meticulous manner, smart dress sense and approach, which earned him the nickname of the “headmaster” at Condé Nast.

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