The bitter break-up between one of Britain's most famous left-wing academics and the Communist Party has been revealed in newly released secret files.
Documents released by the National Archives at Kew show for 20 years the historian and peace campaigner E P Thompson - best known for his ground-breaking social history The Making Of The English Working Class - was the subject of MI5 surveillance.
Professor Thompson, a long-time member of the Communist Party of Great Britain (CPGB), first came to the attention of the security service in 1943 when, as a lieutenant serving in the Army, he baulked at having to produce his military identity card.
"I must get out of here and start fighting fascism abroad, and then come back and fight it here," he told the startled guard who had demanded to see the document.
By 1956 however - following the infamous denunciation of Stalin by his successor Nikita Khrushchev at the 20th Congress of the Soviet Communist Party - Prof Thompson had become profoundly disillusioned with his "comrades" in the CPGB.
In a scathing letter to the secretary of the party's Yorkshire district committee - intercepted by MI5 - he announced that he was quitting the committee having lost confidence in the "political integrity" of the hard left party leadership.
He bitterly castigated members of the party's ruling executive committee (EC) for acting as "high priests interpreting and justifying holy writ as emanating from Stalin" rather than independent Marxists.
"How can one accept the plea of false information and good faith as an excuse for 20 years of uncritical and often hopelessly inaccurate (our opponents would say mendacious) propaganda? Is faith the main quality required of the leadership of the Party of Scientific Socialism," he wrote.
"All I can say is thank God there is no chance of this EC ever having power in Britain: it would destroy in a month every liberty of thought conscience and expression, which it has taken the British people 300-odd years to win.
"And it would do it all with benevolent safety valves and in a smug and supremely self-righteous belief that it was acting in the interests of the working class whose interests it was divinely inspired to interpret."
The MI5 surveillance showed that by the time of the split, his fellow party members had become just as unhappy with their troublesome comrade as he was with them.
A secret recording picked up one member complaining of a meeting in Leeds where some of those involved had "even gone so far as to say that the Soviet Union was not a socialist country".
The report noted: "He said that he thought things would probably end up all right there but he didn't know about Edward Thompson who he thought was the main instigator of it all."
Prof Thompson was suspended from the party after launching a publication with fellow historian John Saville called The Reasoner highlighting his dissident views. He finally resigned altogether in protest at the suppression of the Hungarian uprising by Russian tanks in November 1956.