Britain's former ambassador to Washington has written to John Prescott to say he will not step down as head of the Press Complaints Commission (PCC).
Sir Christopher described several ministers as "political pygmies"
The deputy prime minister had urged Sir Christopher Meyer to resign after he published a book criticising him and other senior politicians.
Mr Prescott also raised questions about his impartiality as PCC chairman.
But Sir Christopher said he did not believe the contents of his book prevented him from doing his job.
In his letter, he said: "I intend to continue to carry out my duties as I have sought to discharge them in the last two and three-quarter years: impartially, independently and effectively."
His book, DC Confidential, serialised in two national newspapers, covers the period from 1997 to 2003, and comments on the build up to war with Iraq.
In it, Sir Christopher dubs several Cabinet ministers as "political pygmies" .
He describes Mr Prescott arriving "at the embassy like a mastiff with his hackles up".
And he notes the deputy prime minister "never appeared to be sufficiently up on these (foreign policy) issues".
At one meeting with a US senator about the former Yugoslavia, Mr Prescott is quoted talking about war in the "Balklands" and "Kovosa".
Publication of the book prompted Mr Prescott to ask Sir Christopher: "How can I or others criticised in your book come to the PCC in future and expect impartiality when you have made it clear you are anything but?
"How can you now hope to be an 'honest broker' at the PCC if people suspect they may feature in any future literary effort on your part?"
He also said: "I am alarmed that you are perfectly happy to profit from tittle-tattle, betraying confidences and by character assassination - the kind of behaviour you at the PCC should be protecting the public from."
But in a detailed rebuttal letter to Mr Prescott, Sir Christopher argued that his book had been submitted to the Cabinet Office for approval.
If the PCC received a complaint about the book or him, he would "follow the well-established practice" of not taking part in considering it "where there is a real or perceived conflict of interest", he said.
Neither he nor his agent had been involved in negotiations with national papers about serialising the book, he said - that job had been done by his publishers.
He added: "In light of the above, I do not believe that the contents of my book prevent me from acting as chairman of the PCC and interpreting the Code of Practice in accordance with past decisions of the Commission."