Foreign Secretary Jack Straw has attacked ex-ambassador Sir Christopher Meyer's memoirs as an "unacceptable" breach of trust.
Sir Christopher is now head of the Press Complaints Commission
Mr Straw said the book raised questions about Sir Christopher's role as head of the Press Complaints Commission.
He rejected the book's claim that the Foreign Office was cut out of much of the discussion before the Iraq war.
Senior civil servants and the Lib Dems have echoed concerns about Sir Christopher breaking confidentiality.
Sir Christopher's book, DC Confidential, details his time as UK ambassador to the US between 1997 and 2003.
He criticises Tony Blair for failing to use his leverage in Washington to delay the Iraq war to allow better planning for the post-Saddam Hussein era.
Jack Straw says Sir Christopher was a marginal player on Iraq
He also says many British ministers who visited the US were political "pygmies" who failed to impress their American counterparts.
Sir Christopher says Mr Straw was "mystifyingly tongue-tied" when as home secretary he met US Attorney General Janet Reno and FBI director Louis Freeh in 1999.
"He was not much better in his early days as foreign secretary," Sir Christopher says.
"With the acquisition of experience, Straw was to develop into a solid and competent foreign secretary, though, as the French say, he did not invent gunpowder."
Sir Christopher was previously press secretary to Sir John Major when he was prime minister and the book details his early morning talks in the Majors' bedroom.
Asked about the book on BBC Radio 4's Today programme, Mr Straw said: "I think it is completely unacceptable for someone like Christopher Meyer to break trust in the way that he has done.
"It undermines the key relationship between civil servants and ministers. It has led to very great concern, I may say, amongst the whole of the diplomatic service."
Mr Straw said he was much angrier about Sir Christopher breaking "personal confidences" he had with Sir John Major and his wife Norma than what he had said about him.
It was "preposterous and demeaning" to discuss the underwear the prime minister was wearing.
Mr Straw said Sir Christopher was not nearly as involved in discussions about Iraq as he now tried to suggest.
He had been a "marginal player" in the negotiations for United Nations resolution 1441, which the UK has used as a main plank of its legal justification for the war.
Mr Straw also suggested a potential conflict of interest, asking how people could complain about the serialisation of the book in two newspapers when Sir Christopher was himself chairman of the Press Complaints Commission (PCC).
Labour MP Alan Keen, a member of the Commons culture committee, said Sir Christopher should consider his position as head of the PCC.
The public would not have confidence in the commission if they knew its chairman had himself released "tittle tattle", he said.
Sir Christopher has not yet responded to his critics but is due to be questioned on the issue next month by the Commons public administration select committee.
A spokesman for the Press Complaints Commission said: "If anyone did complain about the serialisation, then Sir Christopher would not play any part in the investigation or decisions."
And Bob Satchwell, director of the Society of Editors, said the row strengthened the view that Sir Christopher was independent of politicians and the media.
Jonathan Baume from the First Division Association, which represents senior civil servants, said it had been "utterly wrong" to publish the book.
"Whatever Sir Christopher's technical right to publish, his memoirs are a fundamental breach of trust and confidentiality which undermine the relationship between ministers and civil servants and diplomats," he said.
Former Cabinet Secretary Lord Butler has joined the criticism, saying memoirs like Sir Christopher's "inhibited frank conversation" between ministers and officials.
"Chris Meyer is a friend of mine and I've got a very high regard for him, but I must say I think the writing of these books and certainly the publication of them isn't a good idea," he told Radio 4's The Week in Westminster in an interview to be broadcast on Saturday.
The current Cabinet Secretary Sir Gus O'Donnell, the top civil servant, recently said he planned to review the rules on memoirs written by government insiders.