Mother-of-four who tired of the professional juggling act

About 15 years ago, Ruth Kelly and David Miliband had a brief fling when they were both young Labour activists swept up in Tony Blair's grand project to build New Labour.

Yesterday, a suspected political link between the pair, who are close friends, led to a fresh bout of intrigue and speculation in Labour high command.

Was Ms Kelly's decision to step down as Transport Secretary in the imminent cabinet reshuffle a sign of disillusionment with Gordon Brown's leadership and a first move towards backing Mr Miliband's barely-disguised leadership ambitions?

The answer, as with many things to do with Labour's leadership machinations, is complicated. She was once close to Mr Brown but was widely believed to be among the cabinet ministers contemplating resignation to force Mr Brown's out of office. If that succeeded she would almost certainly support Mr Miliband for the leadership.

But her main reason for resigning had less to do with that, and was – perhaps surprisingly for a politician who says she wants to spend more time with their family – exactly that.

Ms Kelly, 40, had finally decided she could no longer perform a gruelling three-dimensional juggling act.

She is a mother of four young children who had to balance family life with the ceaseless demands of ministerial office. She needed to navigate the divisions and personality clashes at the top of the party – a feat she accomplished with consummate skill.

And she had to combine life in Westminster with the pressure of nursing her marginal constituency in the north-west of England.

At a drinks party in July, she insisted she was going to take a month's summer holiday in the Far East with her family – and hoped her holiday destination did not have mobile phone reception. She explained to fellow revelers that it was about time she devoted an unbroken chunk of time to her husband, Derek, and their children.

Her departure from the front line brings an end to a meteoric government career in which she was even touted as a future prime minister.

Friends now expect her to go a step further and announce she will quit as MP at the next election, rather than suffer the humiliation of being ousted from her Bolton West constituency.

Ms Kelly, who previously worked as a Bank of England economist, arrived at Westminster in 1997 heavily pregnant with her eldest son, Eamonn, who was born 11 days after Mr Blair moved into Downing Street.

Three other children followed – Sinead, Roisin and Niamh – but the responsibilities of motherhood did not stop prevent her elevation to the political fast-track.

She unusually managed to find favour with Blairites and Brownites – she served under the future prime minister at the Treasury – and told colleagues she refused to become involved in the faction-fighting.

Ms Kelly reached the Cabinet at the age of 36, making her its youngest member by a decade at the time. But she always insisted on making space for family life, refusing to take home ministerial red boxes.

Her devout Catholicism, with traditional views on abortion and contraception, put her at odds with many contemporaries. She was known to have trouble reconciling her faith with the Human Fertilisation and Embryology Bill, which liberalises stem cell research.

Ms Kelly also rejected demands to break links with Opus Dei, which espouses hardline Catholic views, arguing: "It is a private spiritual life and I don't think it is relevant to my job."

The reshuffle

Going up...?

Jon Cruddas

MP for Dagenham. Enhanced his status during conference. Turned down offer of junior ministerial post last year.

Shaun Woodward

Northern Ireland Secretary. Former Tory MP. Tipped for central role at Cabinet Office or Treasury.

Liam Byrne

Home Office minister. Has handled the sensitive issue of immigration well.

Jim Murphy

As minister for Europe, won Commons approval for EU Treaty of Lisbon.

... Going down?

Geoff Hoon

Labour Chief Whip would like to stay in government but may stand down because of promise to become a European commissioner.

Des Browne

Brown ally who may lose one or both of his two jobs as Defence Secretary and Secretary of State for Scotland to make room for fresh faces.

Paul Murphy

Loyalist who made surprise return to Cabinet when Peter Hain resigned in January as Welsh Secretary. May now return to back benches.