The affair was a well-kept secret: its end has been played in public

They made an unlikely couple. He a 57-year-old, life-long socialist and conviction politician; she the publisher of the right-wing Spectator magazine, newly wed, 13 years his junior.

They made an unlikely couple. He a 57-year-old, life-long socialist and conviction politician; she the publisher of the right-wing Spectator magazine, newly wed, 13 years his junior.

Yet when David Blunkett met Kimberly Quinn at a dinner party in August 2001, something clicked between them.

Despite marrying only nine weeks earlier, Mrs Quinn, better known by her professional name of Fortier, embarked on a three-year affair with the Home Secretary.

It was not until August this year that details of the relationship were leaked to the press. The News of the World splashed the story across its front page under the headline "His love for mum-of-one", but without disclosing the name of Mr Blunkett's lover.

It took The Sun 24 hours to fill in the missing part of the puzzle and identify Mrs Quinn. The story gathered pace and within 48 hours it emerged that the American-born publisher was expecting her second child.

The media feasted on further revelations - by "friends" and "sources" close to the couple - including details of their break-up and claims that Mr Blunkett was the father of Mrs Quinn's two-year-old and an expected second child, due in February. Some publications, including The Independent, have until now largely ignored the affair, which they regarded as a private matter with no significant political implications. But the personal has now spilt into the professional, with the allegation made yesterday that Mr Blunkett abused his position as Home Secretary to fast-track a visa for Mrs Quinn's Filipina nanny. As a result, he has announced that an independent inquiry will investigate the claim.

The accusation, thought to have been leaked by Mrs Quinn, 44, is seen by some as an act of revenge in a bitter and messy end to the affair. Others believe she is trying to head off a paternity battle.

The principals in this extraordinary affair come from very different backgrounds.

Born in Los Angeles, Kimberly and her sister, Jennifer, had privileged childhoods. Kimberly's father, Marvin Solomon, made a fortune in radiation detection equipment, while her mother, Lugene Sanders, was a highly paid television actress.

Kimberly won a place at Vassar College in New York state to study political history, followed by a masters degree at Oxford University. She worked as a secretary to Helen Gurley Brown, founding editor of Cosmopolitan, and moved to Woman's Day in 1983 before becoming editor of Gifts and Decorative Accessories, a trade magazine, a year later. It was around this time that she met the investment banker Michael Fortier, whom she married in 1987.

Mrs Quinn then joined GQ magazine before being poached by Condé Nast in 1994 and then moving to The Spectator in 1996. While her career was taking off, her first marriage was falling apart. Her husband claimed it was largely because she was unfaithful.

It was while she was still married - she divorced in 2000 - that she came to work in the office of Condé Nast in the mid-Nineties, when Stephen Quinn became publishing director of GQ magazine. A relationship blossomed and in May 2001 they became engaged. They married the following month.

Both still flourish in their respective publishing careers - Mr Quinn is best-known as the current publisher of Vogue magazine - and they gained a reputation as a power couple.

But one thing was missing in the relationship: children. In order to start a new family at their Mayfair home, Mr Quinn, who has three children from a previous marriage, agreed to have a vasectomy reversed.

Mr Quinn, now 60, was therefore delighted when his wife became pregnant and, in September 2002, gave birth to a boy they named William.

But it looks increasingly likely that the boy was fathered by David Blunkett.

During the middle of her affair with Mr Blunkett, Mrs Quinn would take her son away for the weekend alone, telling her husband she needed quality time with the toddler. In fact, she was secretly meeting the Home Secretary.

She visited Mr Blunkett at his official residence in London and they spent weekends at his cottage in the Peak District.

Earlier this year, when William was 18 months, Mr Blunkett took Kimberly and the boy on holiday for two weeks to the Greek island of Corfu.

The affair appeared to be proceeding unnoticed and the Quinns announced, a few months ago, that Kimberly was pregnant again.

It was about this time that the News of the World story broke. It also emerged that the secret relationship was coming to an end. Mrs Quinn is said to have wanted to end the affair and try to save her marriage. She believed that Mr Blunkett, who is said to be deeply distressed, indeed "heartbroken", by the end of the affair, leaked details of their relationship in a desperate attempt to destroy her marriage and keep the affair going.

The veracity of this allegation, and others, is difficult to uncover, with both sides refusing to speak publicly.

What is clear, however, is that the soured relationship turned to open conflict when it was reported that Mr Blunkett wanted access rights and had written to Mrs Quinn's solicitors demanding a DNA test on her two-year-old and on the unborn baby.

According to "friends" of Mr Blunkett, the tests are only a formality, because the Home Secretary and his former lover already know that William is a result of their affair. According to the sources, a DNA test last year confirmed that Mr Blunkett is William's father..

Sources described as "friends of the Quinn family" have also apparently conceded that both children are "almost certainly" Mr Blunkett's.

The strength of Mr Blunkett's reaction surprised many. Observers have speculated that the politician's harsh personal experiences may hold the key to his desire to continue the relationship and for access to the children.

While some people believe that Mr Blunkett merely wants the rights of a father, "friends" of Mrs Quinn suggest he is using the issue to try and get back at his estranged lover.

Mrs Quinn's reason for apparently leaking a private e-mail about the alleged political interference to The Sunday Telegraph - whose company also owns The Spectator - is being viewed as revenge. Others interpret the leak as a way to force Mr Blunkett to desist from the paternity challenge.

The e-mail, sent from Mrs Quinn's private Hotmail account, alleges that Mr Blunkett "fast-tracked" a visa application for her former nanny - something the Home Secretary strongly denies. The e-mail ends with the comment: "He's so paranoid he'll think it's me and try and nail me."

The added political dimension to the story, and the threat to Mr Blunkett's political future, prompted the Home Secretary to make his first public response about the affair.

He said: "I am very saddened that someone I cared so deeply for should seek, quite erroneously, to damage my public position.

"This cannot be in the interests of any of us. I shall continue to keep my private life private and separate from my public duties."

Mr Quinn has also spoken for the first time, revealing that he had forgiven his wife. He told the Sunday Times: "I adore my wife and I love William more than I can say. I'll take a bet with you: I won't win the lottery but Kimberly Quinn, William Quinn and his brother - we will all be together for a very long time."

HOW THE STORY EMERGED

14 AUGUST 2004

The News of the World reveals that Blunkett is having an affair with a married woman. Blunkett refuses to discuss it and insists his private life has no bearing on his role as Home Secretary

15 AUGUST

The Sun names the woman as Kimberly Fortier - who has since changed her name to Quinn - the American publisher of The Spectator magazine'

16 AUGUST

Mrs Quinn makes no comment about her private life and asks the media to respect her privacy

17 AUGUST

A newspaper reports that Mrs Quinn is several months pregnant with her second child and is due to give birth early next year

23 NOVEMBER

Mrs Quinn is said to have medical evidence showing the Home Secretary is not the father of her first child

27 NOVEMBER

Mr Blunkett denies allegations that he intervened in the visa application of Mrs Quinn's Filipina nanny, Leoncia "Luz" Casalme