His exceptionally close relationship to Tony Blair led analysts to conclude he was the real deputy prime minister.

Some even suggest that when the prime minister speaks, what you get is pure ‘Campbell’.

Not bad for someone who used to write pornography to make ends meet, and had a nervous breakdown at the age of 29.  

But Campbell, who had hinted already that he wanted to quit, has now given up the struggle for his political survival after being accused of exaggerating the case for war to invade Iraq.

He faced probing questions before the London judicial inquiry into the death of weapons' expert, David Kelly.

And he has been very much on the defensive after launching an attack on the BBC over a report that he "sexed up" a dossier on Iraq.

While intelligence chiefs quizzed by the inquiry generally backed up Campbell's account of events, his reputation as a slippery spin doctor who inadvertently became the centre of the story made him more of a liability than an asset to his close friend, Tony Blair.

Nervous breakdown

After reading modern languages at Cambridge, Campbell, 46, made money by writing pornographic stories for men's magazines.

He then entered journalism and rose to become editor of a national newspaper at the age of 29.

But the publication's launch faltered and the experience led him to have a nervous breakdown.

Soon after, he gave up alcohol and impressively re-established his journalistic career.

Political appointment

A keen Labour supporter, in 1994 he took a massive pay cut to become spokesman for the leader of the opposition, Tony Blair.

Campbell: Ex-alcoholic and
pornographer turned spin doctor

With the Labour election victory in 1997, he became the prime minister's chief press secretary, and set up a formidable media machine to try to control the news agenda.

Campbell's appointment was unlike any before him - a political appointment to a civil service post, with opponents arguing this meant the taxpayer was forking out for a propagandist.

In 2000, Campbell gave up daily briefings to Westminster lobby journalists to concentrate more on long-term strategy.

It was a move prompted by the fear that he, rather than his boss, was becoming the focus of media stories.

Short temper

Campbell's detailed policy knowledge, short temper and - above all – close relationship to Tony Blair have left virtually every member of the government in his shadow.

Whatever the outcome of the Hutton inquiry, historians will judge Campbell's wide-ranging role as immensely significant to Blair’s Labour.

He has presided over a period in the party’s history when it has moved from being viewed with derision by the electorate to two landslide election victories. 

He has changed the way Downing Street press chiefs are seen in the outside world, by becoming a public figure.

And he is closer to his boss than any press chief before him.

Blair has already lost a key confidant and political ally in Peter Mandelson. Now it will be seen whether the going of Campbell will bring the prime minister back into more trusting relationships with his party and the British electorate, or serve to isolate him further.