A confidential report of cabinet meetings, during which ministers approved an attack on Egypt after its nationalisation of the Suez Canal, has been released by the National Archives.
The minutes, handwritten by Cabinet Secretary Sir Norman Brook, show how ministers scrambled to arrange a cover-up following claims of military collusion with Israel and France.
According to the document, the biggest question worrying Prime Minister Sir Anthony Eden at a key Cabinet discussion in October 1956 was whether Israel was prepared to press the trigger that would spark hostilities.
The Prime Minister, whose government had already approved the call-up of British army reservists and prepared the groundwork for war, was in a state of high anxiety about Israel's willingness to take on the Egyptians.
Such an attack was seen as a pretext for British and French forces to step in, supposedly to stop fighting between Israel and Egypt but in effect to seize the canal from the increasingly pro-Soviet government of Gamel Abdel Nasser.
According to Sir Norman's notes, released after more than 50 years, ministerial doubts were reinforced when the Prime Minister said: "It now seems that Israel won't attack. We can't hold our military preparations for more than a week or two. A winter operation would not be satisfactory."
In fact, Israel had its own reasons for taking on Nasser's army.
Egyptian nationalisation of the canal meant that shipping towards or from Israel was blockaded and Egyptian-backed terrorists were launching regular attacks from the Sinai and the Gaza Strip.
British fretting over Israel's resolve proved groundless and the notes showed that ministers in London followed the progress of the Israeli campaign closely. With intelligence reports showing that the Israelis were doing well, the British Prime Minister - who just a few months earlier had declared that it was "appalling to have to fight with Israel versus the Arabs" - told the Cabinet on November 2 that the military position was "very satisfactory".
The Israelis, he said, "are tonight within 12 miles of Port Said, have won a tank battle near Ismalia (and) are opposite the Suez Canal."
Three days later the British made an assault on Port Said having called on the Israelis not to advance to within 10 miles of the canal. But, with the Americans refusing to back the attack, they were forced into a withdrawal. The political repercussions were devastating.
There were calls for an inquiry into whether the government had acted in collusion with Israel and France and President Nasser's image was taking on a heroic tinge in the public mind.
According to Sir Norman, rattled ministers gathered to discuss a plan for a cover-up. They were without doubt that the Prime Minister was suffering, according to the minutes, from "nervous exhaustion".
Sir Norman recorded Viscount David Eccles, the Minister of Works, asking his colleagues: "What line should we take on collusion?"
Minister of Labour and National Service Iain Macleod said that the evidence of collusion was "pretty shoddy. Could we not say [that] of course we knew of Israel's intentions and took precautions accordingly?"
However, he recommended that the government should also say there was "no prior agreement, no promises of territorial changes, and no incitement to Israel to attack."
A month later a still frail Sir Anthony Eden told Parliament: "To say that Her Majesty's Government were engaged in some dishonourable conspiracy is completely untrue - and I must emphatically deny it."