Now it has come to light that British spies looked at an even more audacious way of derailing the man behind the German war machine - by giving him female sex hormones.

Agents planned to smuggle doses of estrogen into his food to make him less aggressive and more like his docile younger sister Paula, who worked as a secretary.

Spies working for the British were close enough to Hitler to have access to his food, said Professor Brian Ford, who discovered the plot. He explained that estrogen was chosen because it was tasteless and would have a slow and subtle effect, meaning it would pass Hitler's food testers unnoticed.