Ruth Kelly’s grandfather Francis, a father of 11 known simply as Master Kelly, taught the children of Altishane Primary near Strabane, Co Tyrone, in the 1930s. His granddaughter, Ruth Maria, was educated at some of England’s most renowned public schools and universities and worked at a national newspaper before being headhunted by the Bank of England. She then broke into politics, becoming one of the youngest Cabinet ministers.

Despite that distance from her beginnings, Ms Kelly has retained a deep fondness for her Irish roots. Her four children — all born since she became an MP, but when Parliament was in recess — are named Eamonn, Sinead, Roisin and Niamh. Like the Prime Minister, she guards her family’s privacy fiercely.

Yesterday the parish priest who married her to Derek Gadd in 1996, Father Digby Samuels, said that she had asked him not to allow reporters to inspect the marriage register at St Patrick’s Church in Wapping, East London.

For a minister in a government which claims to support open government and freedom of information it was an odd approach. The Marriage Act 1949 states that the register can be legally inspected by the public.

Ms Kelly is a devout Roman Catholic and remains very conservative on issues such as abortion and contraception. Her approach to sex education in schools may prove controversial in her new role.

Ms Kelly will not work at either the Department of Health or the Department for International Development because of her staunch Catholicism and stance against contraception.

Born in Limavady, Co Londonderry, in May 1968, she was the youngest of three children. Gertrude Anne, her mother, was a teacher and her father, Bernard James — known to his family as Seamus — ran a chemist shop in nearby Ballykelly.

A year after Ms Kelly’s birth, her father — who died recently at his home in Spain but was buried in Ireland — bought a business in Belfast. Not long afterwards, in the early years of Northern Ireland’s Troubles, they moved again, to the Irish Republic.

When the family relocated again to England Ms Kelly became a pupil at Edgarley Hall, the prep school for Millfield in Somerset, where fees are currently £10,000 a year.

It was one of many schools she attended because her family moved frequently. She took her O levels at the private Sutton High School for Girls in Surrey, passing mathematics, physics, chemistry, biology, English, German, history and religious studies with seven As and a B.

Steve Callaghan, the headmaster, declined to say which subject she slipped in. “I can tell you it wasn’t maths,” he said. “But she is an incredibly important person in education so I don’t want to annoy her.” She won a place at Oxford to read medicine but switched during her first year to politics, philosophy and economics.

A contemporary from Westminster and Oxford remembered: “She was a bit of a bluestocking at school. She had a slightly mousy look and wore her hair in a thick bob.”

After Oxford, she moved to the East End of London — where she met her husband-to-be during an anti-racism campaign — and studied part-time for a masters degree at the London School of Economics.

In 1990 she sent a short, handwritten note to Will Hutton, then economics editor of The Guardian, asking to be his research assistant.

“She was very, very good at economics — economics is the alpha and omega of Ruth Kelly,” Mr Hutton said yesterday. “She was also imbued with a great sense of public purpose and ambitious to have an impact on the world. She’s very principled — she has a moral compass and she runs her life by it.”

Mervyn King, then deputy governor of the Bank of England, headhunted Ms Kelly in 1994 to work on the Inflation Report.

In 1997 she was elected as Labour MP for Bolton West in the landslide that swept Tony Blair into power and was soon making her mark on the Treasury Select Committee.

David Miliband, who has replaced her as Cabinet Office Minister, is a previous boyfriend. He leaves the Education Department as she arrives.

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