The research shows that Fritz Wiedemann, a former chief aide to Adolf Hitler, who recommended him for the Iron Cross and became a father figure to the future dictator had warned the British intelligence when Hitler was at the height of his power.
According to Dr Thomas Weber, a professor at the University of Aberdeen, Wiedemann risked death for his betrayal as he urged Britain "to strike as hard as possible" against the "madman" Hitler after he defeated France in 1940, the 'Daily Mail' reported.
Peace was impossible without the removal of Hitler, claimed Wiedemann.
"The fact that Wiedemann was entirely against Hitler is, up until now, unknown," Weber told Germany's Der Spiegel magazine yesterday.
In 1935 Wiedemann, who was a senior officer in the List Regiment in which Hitler served as a messenger in France and Belgium during WW I, and who put the Austrian corporal's name forward for the Iron Cross First Class for bravery, was appointed as his adjutant.
Wiedemann was a fervent supporter of Hitler in the early years following defeat in 1918 but grew disillusioned with Nazism as time went on.
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In 1939, Hitler sent him to San Francisco as consul general, an exile seen as punishment for his increasing criticism of the party's lust for world domination and his fears of a new global conflict.
Weber says that his research shows that there he met British intelligence's US head Sir William Wiseman after the outbreak of war in September 1939.
Weber has found the records of Wiedemann's talks with him in 1940 in which Wiedemann openly warned against Hitler.
Wiedemann said Hitler had a "split personality and numbered among the most cruel people in the world, saw himself better than Napoleon and that peace with him was impossible."
He warned Wiseman of the Fuhrer's plans to attack and conquer the UK and "recommended strongly" that the British themselves strike as quickly and as "hard as possible" against him.
He also told Wiseman that the morale of the German population and the support of Hitler were lower than generally believed.
Wiedemann offered to publicly denounce the German regime, but the White House at that time had no interest in such an offer as it was not at war with Germany and wanted to keep out of the conflict.
Weber noted that Wiedemann also claimed to Wiseman that he used his influence to protect former Jewish members of the List Regiment from the Gestapo.