In a furious exchange of letters that day, Eisenhower wrote to Eden that his ambassador at the UN was astonished to find Britain obstructing an American attempt to impede the Israelis from attacking Egypt.

(Britain intended to use the attack as a casus belli: so it could "protect" the Canal from an Israel-Egypt war.) In addition to this devious manoeuvre -Eisenhower complains of being "left very much in the dark" -Eden was plainly "violating our pledged word" under the recent 1950 Joint Declaration between America, Britain and France to settle Middle East disputes without force.

Eden said the Declaration was "past history". Eisenhower retorted that Britain's disregard for the Declaration, for the UN, and for international law was incomprehensible. As for Israel, wrote Eisenhower, if it were found to be an aggressor against Egypt "the fat would really be in the fire".

Eden's response was pure Donald Rumsfeld. The UN, he said, was useless and dilatory.

Treaties were out of date in the face of this new security threat. Israel was in perpetual danger from the "ever increasing pressure of certain Arab states". There was no real way of preventing "this volcano from erupting somewhere". In conclusion the Prime Minister could only hope that, perhaps "when the dust settles there may be a chance for our doing a really constructive piece of work together" in the region. He added a sly dig that the President's "constitutional and other difficulties" were inhibiting him from decisive action. Britain would go it alone.

In the last of five letters exchanged on invasion day, October 30, Eisenhower is shocked to receive news of a final Anglo-French ultimatum to Nasser (to leave the Canal Zone on pain of immediate attack) not from Eden personally, but through diplomatic channels. That very morning he had addressed him not just as a Head of Government "but as my long time friend". And this, he protests, "at the very time" when the UN Security Council was considering the matter. America was never told of the collusion with Israel, and Eisenhower was entitled to be very angry.

Eden in turn was bitter. The Soviets, he wrote the following week, had extended their empire into Hungary with no peep from the UN, at the same moment as British forces were landing in Egypt. To Eden, Egypt was a chapter in the Cold War book, not the post-imperial one. This, wrote Eisenhower, was the point. In a post-imperial world, dealing with Russia sometimes required sophistication, not brute force.

By mid-November the two men were clearly beyond letters and were talking regularly by phone. Britain had by then been forced to withdraw from Port Said, giving way to a UN force. In reality Nasser had won. In November, the new British Ambassador to Washington (Sir Harold Caccia) was instructed humiliatingly to deliver his credentials at 7 in the morning.

An increasingly isolated Eden was told he would not be welcome in visiting America. Anglo-American relations were seldom on a worse footing than in November 1956.

Eisenhower later regretted his harsh treatment of Eden during Suez. Dulles even asked the Foreign Secretary, Selwyn Lloyd, on November 18, "Why did you stop? Why did you not go through with it and get Nasser down?". Lloyd's reply spoke volumes, "If you had so much as winked at us we might have gone on". Small wonder Eden could complain on November 7 of "a lack of a clear understanding between our two countries . . . on the Middle East". The letters had apparently not bridged this comprehension gap. Eden even wrote significantly that "It is difficult to come to considered conclusions by correspondence". Two months later Eden resigned, with Nasser triumphant and America not a little gloating.

Boyle's conclusion is that the letters reveal Eisenhower as a shrewd statesman.

Eden held up well in the early months, especially when the Americans were pursuing hare-brained intelligence ploys against the Russians. The President was tactful on decolonization, the Cold War and the formation of the Common Market. He was "a well-informed, intelligent, authoritative leader", says Boyle, and not the lightweight portrayed at the time by the British press.

With Suez, everything collapsed. Experts differ on whether Eisenhower was sufficiently explicit with Eden against the use of force.

Macmillan's advice had been that "Ike will lie doggo". Dulles murmured likewise to Lloyd. Yet the letters are conclusive evidence. When Eisenhower later pondered if he had been less than helpful to an ally, Dulles reasonably pointed out that "it was they who double-crossed us". When British withdrawal was announced, Eisenhower hoped at least that relations could be improved, and that Suez would seem "like a family spat".

Boyle's analysis is plausible, that Suez was a case of the determinist school of international affairs. From the moment that Nasser lobbed his grenade into the Anglo-American relationship, the drama followed an inevitable course. The options facing Eden in the summer of 1956 left him little room for manoeuvre. Eisenhower had even less. America was in no mood to fight another overseas war so soon after Korea and had a clear interest in peace in the Middle East. Boyle's judgement is harsher on Eden's handling of the crisis itself. Having overreacted to Nasser he held back in the misguided hope that America might support him. Collusion with Israel was an unnecessary mistake. Having failed to invade fast, Eden then failed to go the whole hog. It was a politico-military fiasco.