He famously remarked that a week was a long time in politics. Ms Kelly, 37, is learning the brutal truth of that observation.

The Westminster buzz now is all about how long she can survive as Education Secretary, despite almost daily declarations of support from No 10. Each declaration seems only to emphasise her political vulnerability.

The controversy over Paul Reeve could not have come at a worse time. Ms Kelly already feared that her career was on the line in steering the education reforms through the Commons. There has been mounting hostility towards the White Paper among backbench Labour MPs, and to her in some quarters. Unless she wins over the doubters, the Prime Minister faces the humiliation of having to rely on Tory support to win the vote.

Ms Kelly has had a rough 13 months, but she is tougher than she appears; her determination to fight on bolstered by strong religious faith and a powerful social conscience.

A former employer once complimented her intellect by declaring that “economics is the alpha and omega of Ruth Kelly”. In hindsight, however, it looks more like criticism. She has struggled to show that she sees education as being about much more than financial inputs and economic outcomes. The feeling remains that she is in the wrong job — but Mr Blair shows little sign of acknowledging his error.

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