Nigel Morris: How an effortless rise to top became a fast ride to bottom

James Purnell was the quintessential Blairite long before the term was even coined.

As a teenage Oxford undergraduate, he did not spend his summer travelling the globe or serving in a bar. Instead the ambitious Surrey public school product headed to Westminster to work for Labour's fast-rising but little-known employment spokesman, Tony Blair.

When Mr Blair swept into Downing Street in the 1997 New Labour landslide, Purnell was one of the trusted young advisers he took with him. His loyalty was repaid; Mr Blair appointed him to the government just three years after Mr Purnell won his Commons seat.

His upward trajectory could have been halted by the resignation of his political mentor in 2007, but instead Gordon Brown made Mr Purnell culture secretary – and the youngest member of the Cabinet.

His appointment was widely believed at the time to have been a departing demand by Mr Blair to his successor. But Mr Brown's allies insisted he was given the job on his merits and that his appointment was proof of the new Prime Minister's willingness to reach out to all sections of the party.

Their trust in him was underlined by his promotion last year to the politically sensitive post of Work and Pensions Secretary, where he demonstrated his Blairite zeal and political self-confidence by setting about contentious reforms to the benefits system.

When Mr Brown's leadership faced a cabinet whispering campaign 10 months ago, Mr Purnell was touted as a likely person to lead the charge over the top. The move never came although he made clear to friends he would enthusiastically support any attempt by his ally David Miliband, the Foreign Secretary, to seize the crown.

Mr Purnell's rise up the political ladder until last night had been so effortless that he made enemies with his self-assured – some said smug – manner.

His Home Counties background and continuing contact with Mr Blair, to whom he speaks regularly, also provoked hostility.

Some detractors took malicious pleasure from a bizarre episode nearly two years ago when he was "photoshopped" into a picture of Greater Manchester MPs outside a local hospital. It turned out he had been late for the photocall and his image was superimposed on a gap left for him by the Labour colleagues who had been there on time.

To his embarrassment, the controversy erupted just after he had urged the television industry to "get their house in order" after a series of "fake" scandals.

Mr Purnell, 39, also found himself embroiled in the furore over MPs' expenses when the Daily Telegraph claimed he had avoided paying capital gains tax on the sale of his London home. He denied the allegation, maintaining that he was not liable for tax on the property.

Downing Street declared its full confidence in him as the claims broke. Last night it was issuing a very different kind of statement, expressing Mr Brown's "disappointment" in a move that could trigger his downfall.