Minister with long links to Miliband

But earlier this year, as she turned 40, the Transport Secretary made up her mind that she had to end what has been a meteoric Cabinet career.

The importance of children in her life was apparent from the moment her son Eamonn was born 11 days after she took the marginal seat of Bolton West from the Conservatives in 1997.

She rose through the ranks to enter the Cabinet at 36, leapfrogging many of her contemporaries - including David Miliband.

Mr Miliband and Ms Kelly had a brief fling when they were in their twenties and have remained close friends ever since. With current speculation rife about the Foreign Secretary's leadership hopes, her links to him are now bound to come under even greater scrutiny.

However, Ms Kelly's skill has been to straddle different camps and she was one of the few ministers viewed with approval by both the Blair and Brown factions during the first two terms.

A committed moderniser, the Transport Secretary has nevertheless infuriated the more traditional feminists in the Cabinet with her staunch stance on abortion and contraception. Some female colleagues even despaired that she had had a fourth child while in office - a record for any woman minister.

Her son Eamonn, who was sent to a private school because of his particular learning needs, is now 11. She also has a daughter Sinead, nine, Roisin, seven, and Niamh, five.

She has never denied that she has links to Opus Dei, the Roman Catholic prelature made famous in Dan Brown's novel The Da Vinci Code.Ms Kelly rejected calls to break off her links with the group or quit, saying: "It is a private spiritual life and I don't think it is relevant to my job. I am here as a Catholic." But Ms Kelly has never shied away from controversy. As Education Secretary from December 2004 she was engulfed in a row after it emerged that sex offenders were being allowed to teach in schools.

She moved to be Communities Secretary in May 2006 and was accused of destabilising the housing market through the botched introduction of home information packs.

Her tenure as Transport Secretary, from last July, is seen to have been her most successful post though she faces anger among Londoners for pressing ahead with proposals for a third runway at Heathrow.

Born in Limavady, Northern Ireland, she was educated at Sutton High School, Westminster School, Queen's College, Oxford, and the London School of Economics.