At the heart of the affair: the 20 key questions

Why is David Blunkett going to court?

Mr Blunkett, who has three grown-up sons from his first marriage, is seeking access to publisher Kimberly Quinn's two-year-old son, referred to in court as "A". He claims he is the father.

Mrs Quinn does not accept that Mr Blunkett is her son's father, and, should she continue to dispute it, the court will be asked to order its own tests. The Home Secretary is seeking a parental responsibility order, which would establish him as the boy's legal father and give him rights over crucial decisions such as education, religion and medical treatment. He has also applied for a contact order under the 1989 Children Act, which would give him rights to see the child. Though there has been a DNA test which reportedly confirms Mr Blunkett as the father, the court would have to order its own, presuming Mrs Quinn refuses to accept his paternity.

Is it unprecedented for a Home Secretary to appear in court like this?

Yes. No home secretary in recent political history has been involved in such a high-profile and public legal battle. However, in 1993, John Major, who was then prime minister, was on the verge of court action when he launched a libel case against Scallywag magazine over alleged links between him and the caterer Clare Latimer. Mr Major, though, dropped the case after the magazine agreed not to repeat the claims.

Was yesterday's ruling a victory for Mr Blunkett?

Yes. Mrs Quinn had applied for the case to be delayed until April, after the birth of her second child. Mr Blunkett, incidentally, believes he is its father too. Lawyers for Mrs Quinn and her husband, Stephen, publisher of Vogue, said she was unable to participate in the case until April because she is seven months' pregnant. She was unable to give instructions to her legal team and was at "serious risk to her physical and mental health", her lawyers said.

But Mr Blunkett opposed the delay, saying that since the relationship ended, it has been 110 days since he has seen the boy. A district judge ruled against delaying the case, a decision which was upheld on appeal yesterday, allowing Mr Blunkett to proceed with his claim. But there has been no ruling on the central issues: whether Mr Blunkett should be granted access or parental rights.

Does yesterday's case raise a potential conflict of interest?

No, though the situation is a little sticky. According to The Sunday Telegraph, when Mr Blunkett told Mrs Quinn he would be demanding access through the courts, he said: "The law is on my side. I know because I made the law."

This was a reference to an amendment, passed in 2000 when he was education secretary, to the Family Law Reform Act 1969, giving the courts the power to order paternity tests even when the mother refuses consent. But it would be unfair to deny a member of the Government the right to litigate.

Family law is the remit of the minister for Children, Margaret Hodge, at the Department for Education and Skills, and the Department for Constitutional Affairs. Against that, Mr Blunkett is one of the most senior members of the Government and shares collective responsibility for all aspects of policy.

What happens at a family court?

Family courts decide issues such as access to children, parental rights and paternity. The guiding principle is that the interests of the children involved are paramount.

Why is this being played out in public?

It is thought to be unprecedented for such a high-profile case to be aired in open court. Mr Blunkett's lawyers asked for yesterday's ruling to be made public, although that was opposed by Mrs Quinn.

Mr Justice Ryder said he had decided to make his judgment public because of the "wholly inaccurate" material already in the public domain. He said that keeping yesterday's judgment private would have provoked further speculation which would have harmed the interests of the parties involved.

What happens next?

Mr Blunkett and Mrs Quinn will now start conciliation hearings designed to help them reach agreement. The meetings are attended by lawyers, officers of the Children and Family Court Advisory and Support Service (Cafcass) and a judge.

If that proves impossible, the court will be asked to order paternity tests, and then to decide on the basis of those results.

Will the rest of the legal battle be aired in public?

Probably not. Mr Justice Ryder made it clear that it did not mean future hearings or judgments would be held in public.

How did the story first leak?

The News of the World revealed in August that Mr Blunkett was having an affair with a married woman, named the next day in The Sun as Kimberly Fortier, who has since taken her husband's name.

On Thursday, Mrs Quinn's magazine The Spectator openly accused Mr Blunkett of leaking the story to the News of the World.

The magazine accused him of "bleating to the tabloid newspapers with the sole object of shocking and humiliating his lover's husband and destroying her marriage". Home Office sources have denied leaking the story.

Many newspapers decided not to report the details when news of the affair first broke. What has changed?

The Independent and other newspapers largely ignored the affair, which they regarded as a private matter. Then six days ago The Sunday Telegraph published details of a leaked e-mail from Mrs Quinn claiming Mr Blunkett used his powers to fast-track a visa for her nanny. She also claimed Mr Blunkett had given her two first-class rail tickets intended for his work as an MP and allowed her to travel in a government car to his home in Derbyshire. So the allegations turned into a very public political row.

How is Mr Blunkett alleged to have helped Mrs Quinn's nanny?

He is accused of fast-tracking an application by the Quinns' Filipina nanny, Leoncia Casalme, for indefinite leave to remain in Britain last year. He had Ms Casalme's application read to him to see whether it was in order.

Soon afterwards, it was put into the system and approved at relatively high speed; documents obtained by the Daily Mail yesterday discovered that just 19 days elapsed between Ms Casalme being told she could wait a year for the passport and it being approved. It was also issued (just) before the usual four-year period foreigners have to work in Britain before they qualify.

He vehemently denies the accusation, insisting the nanny's form was returned to Mrs Quinn and that he took no further part in the process. He says it was "not unusual" for such applications to go through quickly in 2003.

Sir Alan Budd, a former Treasury economic adviser, was appointed to examine whether Mr Blunkett abused his power by interfering in the decision.

Is any of this a hanging offence?

Unlikely. He vehemently denies breaking the rules over Ms Casalme's visa application and insists the Home Office has dealt with the other claims made by Mrs Quinn. Mr Blunkett has paid back the rail fare and apologised for what he says was a mistake in good faith

What happened between Mr Blunkett and Mrs Quinn?

Mr Blunkett appears to have regarded Mrs Quinn as his partner, notwithstanding that she was married to someone else - and several times tried to persuade her to marry him. According to one version, he believed that would happen, and that the children were deliberately conceived, to form their future family unit. But their love affair broke down earlier this year. Mr Blunkett's possessiveness was cited in some newspapers.

What happened between Mrs Quinn and her husband?

Mrs Quinn has enjoyed staunch backing from Stephen, despite the huge publicity surrounding her affair. He had his vasectomy reversed in order for his wife to become pregnant, and they had also undergone fertility treatment. At this time, it appears, she was also sleeping with Mr Blunkett.He appears to have forgiven his wife, and is determined to stay together.

Do we have a right to know what has gone on behind closed doors?

To some extent, when the case raises genuine questions about the conduct of one of the Government's most senior figures. Mr Blunkett faces a series of claims about the use of his office and has set up an official inquiry to look at the most serious of the allegations.

He is entitled to privacy in family hearings like anyone else, but has taken the highly unusual step of asking for yesterday's judgment to be made public. But many newspapers, like The Independent, feel uncomfortable dealing with the more private matters in this case, even though the affair has an important public dimension.

Is Mr Blunkett showing a lack of judgement that throws doubt on his credibility as Home Secretary?

Not necessarily. Mr Blunkett has the staunch backing of colleagues from the Prime Minister downwards. But if he leaked the tale as a matter of revenge that is a serious issue.

How did yesterday's case go down in Downing Street?

Tony Blair's official spokesman said he remained fully confident that Mr Blunkett could continue doing his demanding job. He said: "You simply have to look at what David Blunkett has been doing during the past 10 days in setting out the vision contained in the Queen's Speech, in following that vision through in media appearances and in his work at Cabinet and in his department."

The Chancellor Gordon Brown told GMTV: "He is not being diverted from continuing to do every aspect of his job. I have never seen a situation where David has been prevented from making the difficult and sometimes very tough decisions that a Home Secretary has got to make."

Will Mr Blunkett survive?

Some ministers think Mr Blunkett should drop his court case because it will merely prolong his agony and fuel the dispute with Mrs Quinn, although the Home Secretary seems determined to press ahead, regardless of the cost. But they are adamant that it would be a disaster for the Government if he steps down and still expect him to weather the storm.

Isn't all this a little different from how it used to be?

It certainly marks a major reversal - a government minister trying to prove he is the father of his mistress's child.

What of the victims in this?

It is hard to see how the furore will not impinge on the little boy. Family court proceedings regard the interests of children as paramount. Yesterday Mr Justice Ryder said: "Neither party asks this court for protection from public comment, but 'A' is entitled to enjoy his private life. ... Even public figures are entitled to the civilised courtesies of being ordinary citizens."