Tony Blair's closest aides had "severe moments of doubt" about the invasion of Iraq, according to the diaries of his former media chief Alastair Campbell.
But if the then-prime minister had his own doubts, "he had hidden them from us", The Blair Years diaries say.
In Cabinet the day before the crucial Commons vote on military action, John Prescott and John Reid "looked physically sick", the book also says.
The book's publication comes less than two weeks after Mr Blair left office.
The book describes the Cabinet meeting the day before the MPs' vote in 2003 and following Commons Leader Robin Cook's resignation over Iraq.
Mr Reid, who stepped down at the same time as Mr Blair, warned ministers "we will be judged by the Iraq that replaces Saddam's Iraq, and by the Middle East".
'No going back'
Clare Short told the meeting that she was "going to have my little agonising overnight. I owe it to you".
She did not resign at that time, but did resign as international development secretary several weeks later in protest at the plans for Iraq's reconstruction.
The government won the March 2003 Commons vote despite the rebellion of 139 Labour MPs.
Mr Campbell writes: "All of us, I think, had had pretty severe moments of doubt but he [Mr Blair] hadn't really, or if he had he had hidden them even from us.
"Now there was no going back at all."
Extracts released by Mr Campbell before the 794-page book's publication also includes US President George Bush's decision in September 2002, following pressure from the UK, to seek a fresh United Nations resolution against Iraq.
Mr Campbell writes: "Bush joked to me, 'I suppose you can tell the story of how Tony flew in and pulled the crazed unilateralist back from the brink.'"
The diaries suggest that the president was "far more impressive close up".
The former No 10 director of communications told the BBC that going to war with Iraq had been the "most difficult decision" of Mr Blair's life.
But the decision was "driven by the right motives", he said.
He also revealed that in 2002 Mr Blair was considering resigning before the 2005 general election.
Mr Campbell has admitted removing references to Gordon Brown to stop Tory leader David Cameron thinking he had "a gold-mine to use against the new Labour prime minister".
The book leaves out much detail of the relationship between Mr Brown and Mr Blair - Mr Campbell told BBC Radio 4's Today programme these diaries were "the first chapter of a record that I intend to put into the public domain".
Asked if he was to blame for the breakdown in relations between Downing Street and much of the media during the 10 years Mr Blair has been prime minister, he said there had been "extraordinary expectations" at first, but that "politics is not about euphoria or elation".
Mr Campbell was also critical of much of the coverage of politics: "The media, I think now... the centre of gravity has gone to a place where they only do hero or zero."
Asked about rows with journalists, he said: "I've never really worked out why I provoked such strong reactions."