He was also the traitor who Britain forgot, his treason not so much covered up as politely ignored. When his name was mentioned it was in whispers. His younger brother Julian, now Lord Amery of Lustleigh, hardly mentions John in his autobiography. Fifty years on, he still declines to discuss his brother.
But according to the official papers, at the end of 1945 Julian Amery desperately tramped Madrid, vainly seeking proof that his brother was a Spanish citizen. As such, he could not be tried for betraying Britain. That Julian had just fought a heroic war against the Axis added poignancy to his task.
Their father was Leo Amery, who had been Churchill's Secretary of State for India and who, after John's death, wrote a pamphlet claiming that everything his son had done was "inspired by a desire to save the British Empire".
John Amery's alleged concern for the Empire led him down strange roads. After a wild and ruinous career on the fringes of the British film industry, he became an anti-Semite and fascist. In 1936 he was declared bankrupt, fled to Europe with an actress, Una Wing, whom he married and then abandoned, later taking up with a Frenchwoman called Jeannine Bard. He plotted with the French far right, ran guns for Franco, broadcast propaganda for Hitler and Mussolini and tried to raise a "Legion of St George" of Britons to fight for Germany.
But Amery was not one of Hitler's star turns. He and Jeannine caroused their way around wartime Berlin - and sent the bills to Hitler's private office. When she choked to death on her own vomit in 1943, John narrowly escaped a charge of manslaughter. Within weeks he had found another mistress.
His dismal career came to an end in April 1945 when he and his amorata were picked up by Italian partisans near Como, where John had been conferring with Mussolini. He was handed over to the British military and interrogated, giving an extraordinary, rambling, self-deluding confession-cum-statement. He seemed to have no idea of the gravity of his situation, probably believing that the Amery family would somehow bail him out.
Flown back to Britain, he was charged under the Treason Act, arraigned at Bow Street Magistrates Court and committed for trial.
What Leo Amery failed to describe in his pamphlet were the desperate efforts the family made to save John from the gallows. As is now known from the official documents released last week, Leo Amery hired some of the best psychiatrists in the land to testify that his oldest son was mad. The doctors were in no doubt that John was suffering from a "severe and long-standing case of psychopathic mental disorder of a near psychotic insane type", and was thus not fit to be tried. The government's lawyers, however, would not accept the defence.
Meanwhile Julian Amery had been dispatched to Spain to establish that John was not a British subject. John claimed that during the Spanish civil war, he had become a Spanish citizen and thus could not be charged with treason. But Julian found the Spaniards unhelpful. The Franco regime, it is clear, wanted nothing to do with their one-time gun runner. On 26 November, two days before Amery was due to go on trial in London, it confirmed that he had taken steps to become a Spanish citizen but had never been "inscribed in the Register of Nationalities" as a Spaniard. Therefore, "Mr John Amery does not enjoy the rights and privileges inherent to Spanish nationality."
It was Amery's ruin. With the British Crown refusing to accept a plea of insanity and the Spanish government refusing to accept him as a Spaniard, he had no defence. His trial at the Old Bailey on 28 November 1945 lasted exactly eight minutes. No jury was called and no witnesses were cross- examined. After a brief consultation with his lawyer, Amery pleaded guilty - despite being warned by the judge that a guilty plea meant death. Under the Treason Act of 1351 there was no alternative, and he was duly sentenced to be hanged.
With all hope lost, Amery's "madness" fell away. According to Leo Amery, his son confronted his last weeks with "unwavering serenity and even cheerfulness". He was hanged at Wandsworth Prison on the morning of 19 December, aged 33.
Like a true English gentleman, he "walked unassisted to his fate after thanking the prison chaplain and warders for their unfailing courtesy". His executioner was Albert Pierrepoint, who described John Amery as one of the bravest men he ever killed.