The offer to kill Hitler in a suicide mission was made by Eddie Chapman, a professional criminal and safe-breaker who was trained by the Nazis as a spy and went on to become one of Britain’s most successful double agents, codenamed Agent Zigzag.

Chapman was serving a sentence in Jersey prison for burglary when the Nazis invaded the Channel Islands in June 1940. He was recruited by the Abwehr, German military intelligence, and parachuted into Britain in December 1941. He immediately defected to MI5, the British security service.

Under interrogation by MI5, the 27-year-old Chapman said that he wanted to return to Germany as a double agent, and then kill the Führer by exploding a bomb at a Nazi rally.

Files recently declassified by MI5 reveal an extraordinary conversation between Chapman and Ronnie Reed, his case officer. Reed pointed out that any attempt to kill Hitler would be suicidal: “Whether or not you succeeded, you would be liquidated immediately,” he said.

“Ah, but what a way out,” Chapman replied.

Chapman explained that his German spymaster, an Abwehr officer he knew only as “Dr Graumann”, had promised to take him to a Nazi rally if he completed his mission in Britain successfully, and place him “in the first or second row”, near Hitler’s podium, if necessary by dressing him in the uniform of a senior German officer.

“He believes I am pro-Nazi,” Chapman told Reed. “I believe Dr Graumann will keep his promise. Then I will assassinate Hitler . . . with my knowledge of explosives and incendiary material, it should be possible.”

Reed was convinced that Chapman’s offer was serious, and reported back to his MI5 superiors: “He can think of no better way of leaving this life than to have his name prominently featured throughout the world’s press, and to be immortalised in history books for all time.” Reed believed Chapman was also motivated by an intense patriotism, and a desire to make amends for his criminal past.

The offer would certainly have been brought to the attention of Winston Churchill — the Prime Minister took a personal interest in the Zigzag case and asked to kept informed of developments — but for reasons that have never been fully explained, the opportunity to kill Hitler was rejected.

Professor M.R.D. Foot, the distinguished historian of the Second World War, believes that the decision may have sprung from a number of factors, including a longstanding government policy against assassinating foreign heads of state, and mistrust of Chapman, a notorious jailbird.

“SOE [Special Operations Executive] hatched a plot to assassinate Hitler in 1944, but that, too, was rejected,” Professor Foot said. “Partly because it was believed to be impossible to get an armed agent into Hitler’s presence, and partly because it was thought that Hitler was more use alive than dead, since at that point his strategy was clearly so erratic.”

Chapman did return to Germany as a double agent, but was expressly told “not to undertake any wild enterprises” by his British spymaster, Colonel Tommy “Tar” Robertson.

Chapman convinced the Germans that he had carried out his mission on British soil and was awarded the Iron Cross for his “outstanding zeal and success”, becoming the only Briton to receive the medal. He was parachuted back into Britain in 1944, and took part in a successful deception operation to misdirect the V1 flying bombs.

MI5 has now released 1,800 pages of documents from the Chapman case. The last of the Zigzag files, including information relating to Chapman’s assassination plot, was transferred to the National Archives last month.

The new evidence suggests that the German spymaster “Dr Graumann”, whose real name was Stephan von Gröning, may have been deliberately setting Chapman up as an assassin. Like many Abwehr officers, he was secretly a bitter opponent of Hitler. His offer to smuggle Chapman into a Nazi rally suggests he knew what Chapman had in mind, and that the two men may have been in league.

Chapman survived the war, fêted by both sides, and received an unofficial pardon for his numerous prewar crimes. He died in 1997.

One factor in the decision not to use Chapman as an assassin may have been the horrific reprisals that followed the assassination of Reinhard Heydrich, Hitler’s potential successor, by British-trained Czech partisans in May 1942. But in the end, the idea may have been quashed because Chapman — “an associate of thieves” in the words of one MI5 officer — was simply not the sort of person to be deployed on such a mission. “There was a feeling in the British Establishment that you don’t trust someone who has been in jug,” Professor Foot said.

Exclusive extracts tomorrow in times2 Agent Zigzag — The True Wartime Story of Eddie Chapman, Lover, Betrayer, Hero, Spy, by Ben Macintyre

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