By Ollie Stone-Lee
Political reporter, BBC News website
The sick leader of a declining power is the prevailing verdict of the history books on Sir Anthony Eden.
Eden: Years of pain-killers and stimulants
He entered Downing Street as Churchill's dashing and glamourous natural successor and a man who had stood up against appeasement in the 1930s.
He left an ill man taking refuge at James Bond writer Ian Fleming's Caribbean home with his reputation in tatters, the man whose decision to invade Suez had humiliated his country.
Egyptian leader Gamal Abdel Nasser's decision to nationalise the Suez Canal - the gateway to India and the East - on 26 July 1956 was to become the defining moment of his career.
Eden was outraged. He had personally negotiated the most recent Suez Canal treaty in 1936.
But his fears went further into what many have seen as an obsession with the threat of Nasser.
Eden compared Nasser to Hitler, as did Labour leader Hugh Gaitskell, and particularly to Mussolini.
His fears about Nasser's brand of Arab nationalism were infected with greater worries about the power of the Soviet Union.
In a letter to US President Dwight Eisenhower he wrote: "There is no doubt in our minds that Nasser, whether he likes it or not, is now effectively in Russian hands, just as Mussolini was in Hitler's.
"It would be as ineffective to show weakness to Nasser now in order to placate him as it was to show weakness to Mussolini."
Eden also told a Tory backbencher he found it strange that so few people compared the Suez crisis to 1938.
Egypt might be no Germany but Russia was and Egypt was Moscow's "pawn", he wrote.
"Yet so many seem to fail to see this and give Nasser almost as much trust as others gave Hitler years ago," he went on.
All this theorising about the threat was accompanied by erratic, restless behaviour, according to some of those at the heart of Eden's government.
It is the 50th anniversary of Nasser nationalising the canal
Anthony Nutting, a Foreign Office Minister who resigned over Suez, claimed Eden had shouted at him over the telephone about talk of isolating or neutralising Nasser.
"I want him destroyed, can't you understand?" Eden apparently said.
But a foreign secretary from a later era, David Owen, who worked as a doctor, is among those who have argued that Eden's ill health had a significant effect on his judgement at this time of pressure.
Lord Owen points to how Eden had a gall bladder operation in 1953 which went badly wrong.
It is widely thought that the knife "slipped" and his bile duct cut, resulting in years of abdominal pain.
His biographer, DR Thorpe, points to how Eden's use of drugs against the pain increased in the ensuing years. And he took amphetamines and barbituarates to counteract the side effects of the drugs.
Sir Peter Tapsell says Eden's mistake was tactical
Eden's diaries tell how he sometimes felt wretched after a poor night's sleep because of his pain.
They suggest he consulted doctors at least 10 times between Nasser nationalising the Suez Canal and the end of October, as he was making secret plans for the Anglo-French invasion.
Robert Carr, who served as Eden's principal private secretary, has said: "I find it difficult to accept the judgement that Anthony's health did not have a decisive influence at least on the conduct of his policy."
But current Conservative MP Sir Peter Tapsell, who was Eden's personal assistant during the 1955 election, thinks it is too simplistic to say his illness affected his judgement.
Sir Peter did not have personal contact with Eden during the Suez crisis but watched events closely from his vantage point at the Conservative Research Department.
He recalls Eden looking "completely calm and collected" in the face of "appalling" scenes in the House of Commons.
Sir Peter does not think Eden saw Nasser as a new Hitler.
"He did see - and quite rightly - that Nasser posed a tremendous threat to Britain, and indeed to the West because the Suez Canal was of vital importance," he told BBC News.
"In those days, all oil for Britain and indeed Europe came through the canal and it had been accepted by everybody ever since the canal was built that it was vital for Britain."
Sir Peter believes Eden's mistake was a tactical one - his secret plan for colluding with Israel over the invasion.
But he also suggests the British prime minister failed to appreciate that the Americans were not prepared for anything to happen against Nasser at least until after that autumn's US presidential elections.
Sir Peter says there was a personal lack of connection between Eden and US Secretary of State John Foster Dulles, whom Eden disliked.
It was perhaps this that sealed Eden's fate - he resigned in January 1957.
The Suez invasion may have been a folly, but it was the pressure from the US Treasury on the pound which forced him to accept a ceasefire and proved the ultimate humiliation.