Blood is spurting from Sir Christopher Meyer’s lip as he opens the door to his house in this most civilised corner of Chelsea. “Don’t worry,” he booms, “Jack Straw has not flown back from Iraq to punch me; it was just a shaving accident.”

It is a necessary clarification. Earlier in the day the foreign secretary had been on air denouncing Meyer, our man in Washington in the run-up to the Iraq war, for having the temerity to publish his memoirs. Straw’s hatchet job might not have been purely professional: in his book Meyer had averred that Straw did not always carry the authority of the prime minister and was variously tongue-tied and terrified of Donald Rumsfeld, the US defence secretary. But the straw that might have broken Jack’s back was Meyer trampling over him as “someone more to be liked than admired”. Ouch.

DC Confidential is an insider’s account of Tony Blair’s rush to war; a “kill-and-tell” if you like. It is wounding, not due to its barbs but because of its very reasonableness: Meyer is that dying breed, a supporter of the invasion who was driven to distraction by how badly Blair played his hand in negotiations with President George W Bush.

Listening to establishment condemnations of Meyer as a treacherous servant, the uninitiated might assume him to be a Kim Philby, or at least a Paul Burrell. But Meyer is unrepentant: he rejects Straw’s call for him to stand down as chairman of the Press Complaints Commission, which regulates us inky guttersnipes, and accuses ministers of hypocrisy in condemning his book while “not hesitating to contribute” to biographies of themselves. Oh, he also declares that Blair’ s administration has the sickly “smell” of the declining years of John Major’s premiership. And Meyer should know: he was Major’s spokesman.

He tells a story of Peter Mandelson, glowing from new Labour’s first victory in 1997, asking Meyer how Major had allowed himself to be destroyed by his own side; Blair, Mandelson boasted, would not make the same mistake. Meyer smiled: “Just wait for the stormy weather.” And so it is proving; as Meyer reflects from his living room sofa: “When a government loses its morale the first thing that goes is the discipline.”

Talking of storms, this interview is potentially a bit blowy for me, too: I once had to apologise to Lady Meyer for falsely accusing her of being German (she is half-French and half-Russian and also a British citizen). But Meyer laughs it off with considerable charm: “Don’t worry, Jasp.” You can see Meyer successfully wooing Washington, striking up something close to friendship with Bush.

But, Sir Christopher, surely it is not terribly diplomatic for a former ambassador to write a book that, to pick a random insult, describes the painful courting of Geoff Hoon, then Britain’s defence secretary, and Rumsfeld as resembling a pair of pandas mating? “I have never known what ‘diplomatic’ means entirely,” he says, a smile snaking round a bloodied lip. “According to Jack Straw, civil servants have to remain mute while cabinet ministers such as David Blunkett use a biography to make the most trenchant comments about colleagues. There should be the same rules for politicians and civil servants.”

Meyer says he obeyed the rules meticulously, submitting his manuscript to the Cabinet Office. A fortnight later, after consulting Straw’s Foreign Office, it told Meyer’s publisher that it would not object; nor would the government be making any comment. “You can’t clear a book and then call it a breach of trust,” reasons Meyer. “When politicians have no inhibitions about writing diaries, I just don’t think it right or fair to have a blanket ban on civil servants.”

Straw deflected attention from Meyer’s substantive criticisms of Blair and himself by saying that the ones Meyer had really betrayed were “John and Norma Major”. Ah, so touching that Straw should ride to the defence of the Tories. He was presumably referring to Meyer’s fairly harmless anecdote that he used to brief Major while the prime minister was still in his underpants and Norma in bed.

Straw went on to argue that by invading the privacy of the politicos, Meyer cannot now continue at the press watchdog where he adjudicates on privacy questions. “Good old Jack,” Meyer says sarcastically, imitating a boxer, as if to intimate that the foreign secretary is behaving like a dirty street fighter. “It is a cheap shot. There is no conflict of interest.”

Meyer says he will stand aside as PCC chairman while any complaints arising from his book are adjudicated on. It seems that he will not resign. “Christ, no,” he says sternly. “And I can exclusively reveal there will be no follow-up called PCC Confidential.”

Let us not play the government’s game by focusing on Meyer’s job: let us examine how Blair does his. Meyer sketches a portrait of a prime minister swept away by presidential cavalcades and communiqués; and, indeed, by his own rhetoric. Meyer writes: “There comes a point where, if you hug too close, it becomes an end in itself.” Did it with Blair? “Up to a point, yes.”

Meyer says he told Blair he had “leverage” with Bush because Americans always like a “posse”; Meyer had been told Britain was the only member of the posse who mattered. Still Blair failed to insist on a post-invasion strategy for Iraq, even though Meyer says he warned him that the Pentagon had no feasible plan. Blair, it seems, was too busy trying to sway us to support war with his dodgy dossiers.