The curiously outspoken letter to Tony Blair from 52 eminent diplomats is undeniably a blockbuster. These are men and women who have risen to the peak of their profession by keeping their doubts about the policies of their political masters to themselves, or at least confined to a very tight circle. But powerful though it is, their open letter is no more than a contribution to a debate that is well underway. To this spectator they haven't gone far enough. The issue we ought to be debating is not just British policy in the Middle East, but our close association with the US.
The special relationship has been the foundation of Britain's foreign policy for too long. The second world war ended nearly 60 years ago. The cold war is also over. We no longer depend on the US to save the pound. We have other sometimes conflicting ties. Like Europe - our destiny, Tony Blair told the Commons on Tuesday, lies in the heart of Europe.
Even its admirers admit that the special relationship can never be an equal one. More important is that America's purposes in the world change, along with American presidencies. With the result that every so often our ties with Washington take us into uncharted waters, into dangers we wouldn't venture into on our own. Most obviously, Iraq.
An American writer (I can't remember who) has said that the outstanding American presidents - Franklin D Roosevelt, Harry Truman, John Kennedy - have always defined America's purpose in the world in terms countries like ours can buy into. On some of these we've moved at different speeds, but on the whole we've moved in the same direction.
So what about today? Under Bush and his inner circle (Cheney, Rumsfeld, Perle and company), America sees its place in the world from a more self-interested perspective than ever before.
Preserving its pre-eminence has become national doctrine. True, the state Iraq is in has prompted a suddenly less dismissive attitude in the Bush White House to the United Nations. However, it's clearly driven by the need to find others to share the burden and the dangers. In other words, it's a tactical move, if not a blatant attempt to dump the burden in the UN's collective lap.
In the past there have been rare occasions when British leaders, Conservative and Labour, broke away from the special relationship. I can think of only two such rebels.
The first was Anthony Eden, foreign secretary in 1954, when the French were facing defeat by the Vietminh in Indochina. That year, the foreign ministers of the great powers met in Geneva to try and prevent that colonial war from turning into a big one. John Foster Dulles, the US secretary of state who walked out after a week, was provoked by Eden's flat refusal to agree to an Anglo-American military intervention on France's side.
The second, and I think last British leader to kick against the pricks, was Harold Wilson 10 years later. As is well known, Wilson repeatedly rejected President Johnson's demand that he support America's war in Vietnam by sending out a contingent of ground troops. He also had the temerity - privately - to try and challenge Johnson over the bombing of North Vietnam. It's worth remembering that those were the days of perennial sterling crises.
As the number of US troops in Vietnam reached 150,000, a note to Johnson from his principal aide, McGeorge Bundy, said this: "We want to make very sure that the British get it into their heads that it makes no sense for us to rescue the pound while there is no British flag in Vietnam."
Johnson never forgave Wilson for opposing him. I was in Washington when Wilson made what I think was his last visit. There was the obligatory banquet in his honor, and British correspondents were invited to the White House - not for the meal, but to watch the entertainment. Johnson had chosen an opera star and the song he was to sing. It was I Got Plenty o' Nuttin from Porgy and Bess.
Though he was under great pressure from the left, Wilson refused to denounce American policy in Vietnam. There was too much at stake and, besides, it wouldn't have made a difference. As co-chair of the Geneva conference, he tried hard to mediate to end the war. Consistently the Johnson administration cut him out. What he was doing was questioning America's judgment.
The diplomats end their letter with an appeal to Tony Blair to exploit the influence he currently enjoys in Washington and to withhold Britain's support if his advice is unwelcome or unacceptable. But can Britain withdraw its support? For that it's surely too late. What we can do is to be more wary of American judgment in future - and stop treating the special relationship as holy writ.
· Charles Wheeler is a journalist, broadcaster and former BBC foreign correspondent.
© Guardian Newspapers Limited 2004