A British spy and close friend of Winston Churchill was deeply implicated in the Zinoviev Letter, the most notorious political forgery in British history.
The publication of a letter purporting to be from Soviet officials four days before the 1924 general election helped to sweep Ramsay MacDonald's government from power. But the correspondence mobilising "sympathetic forces" in Labour was later found to be a fake.
Now a new official history, based on access to closed intelligence files, suggests the document was a "dirty tricks" operation by the Secret Intelligence Service (SIS), overseen by Major Desmond Morton. Morton, a First World War hero whom Churchill befriended in the trenches, became an SIS officer on his recommendation and went on to become the war leader's "spymaster". In the early years of the Second World War, he was a trusted fixer within the inner circle of Churchill's bunker.
His role was recently lauded in the film The Gathering Storm, in which Morton, played by Jim Broadbent, is shown leaking intelligence on German preparations for war to Churchill during his "wilderness years".
The truth, however, appears to be rather less heroic. Gill Bennett, until recently chief historian at the Foreign Office, has found that Morton was "centre stage from the beginning" of one of Britain's worst political scandals.
It was Morton who first received the letter, purporting to be from Grigori Zinoviev, president of the Comintern, the internal communist organisation, from an agent in Riga, Latvia. It called on British Communists to mobilise the Labour Party to support an Anglo-Soviet treaty.
Ms Bennett hints that Morton helped to ensure the letter ended up in the Daily Mail, which ran the story under the headline: "Civil war plot by Socialists' masters: Moscow orders to our Reds; great plot disclosed".
Although Ms Bennett believes it possible that Morton initially thought the letter was genuine, she has found he later covered up evidence that it was a fake.
"It might be that since he detested the Bolsheviks and the Labour government, he welcomed the chance to throw a spanner in the works," said Ms Bennett. The author of Churchill's Man of Mystery says there is no evidence suggesting that Churchill was involved.
Nor is there much to support the myth of Morton as Churchill's "mole" in the 1930s. Appropriately for a spy, the truth is more complicated, she said. He appears to have been a trusted fixer, seen by Churchill as clever and loyal but organisationally incompetent.
He was eased out of influence in the latter part of the war and, towards the end of his life, wrote that Churchill was "the most egocentric man I have ever known" whose "ruthless use of power horrified me".
Ms Bennett said of her subject: "When I first began researching Morton I was a little depressed to find that almost everything he was supposed to have done in fact he did not do. But then I found that it is only through Morton that one is able to uncover many of the most intriguing episodes in UK intelligence."
'Churchill's Man of Mystery: Desmond Morton and the World of Intelligence' is published by Routledge on 18 October