The first extracts of Mr Campbell's diaries will be published this year

The ex-spin doctor was reportedly paid �1m for his diaries, although his publishers Random House insist this is "wide of the mark".

The exact date of publication will depend on when Tony Blair quits, which he has said will happen by the autumn.

Passages from the diaries were read out during 2003's Hutton inquiry prompting speculation about a bidding war.

Selected extracts of the two million words of entries will be disclosed first in a book titled The Blair Years, with the full daily entries to follow, the publishers said.

How much will be revealed in the first volume is open to question, as Mr Campbell pledged last year not to rush into print with anything that could damage the Labour Party or the government.

'Daily obsession'

In a letter to the public accounts select committee, he said: "I would consider it wrong to publish in a manner or at a time detrimental to the interests of the government or the party I served."

The focus is very much on Tony Blair himself, and some of the key issues and events during his 13 years as Labour leader Alastair Campbell Campbell diaries extracts

The committee has been critical of former civil servants, ambassadors and political aides who publish memoirs that embarrass the government.

But the full version of Mr Campbell's diaries promise to be one on the most explosive political books of recent times.

"I have kept a diary at various points in my life but when I started working for Tony, an occasional habit became something of a daily obsession, which continues," he said.

"I hope it helps to paint a rounded picture of a man of enormous drive and vision, who has been determined to use his time in power to make a difference and has brought about a lot of change for the better.

"The diary records what I saw, said, heard, thought, felt and did during many of the key moments of his leadership.

"It records good days and bad days. Things going wrong as well as things going right. Moments of disagreement as well as moments of harmony and accord.

"The good moods and the bad moods, usually his the former and mine the latter."

History

Mr Campbell was at Mr Blair's side from shortly after he became Labour leader in 1994 until 2003 when he quit Number 10.

He said he was determined to play his part in shaping historians' views of Mr Blair's time in office.

"The focus is very much on Tony Blair himself, and some of the key issues and events during his 13 years as Labour leader."

Susan Sandon, managing director of the Random House division publishing The Blair Years, said they would be "the political publishing event of the decade".

Tony Blair is expected to be bombarded with lucrative offers from publishers following his departure from Downing Street.

But he revealed last month, in a podcast interview with actor Stephen Fry, that he would not be able to draw on extracts from a diary as he had not kept one.