A distinguished Polish pilot admitted he lied that he found a bomb intended to blow up the plane of Poland's wartime leader, but the episode was hushed up by Britain's government, secret files released on Monday showed.
The apparent plot to assassinate General Wladyslaw Sikorski, who led the Polish government in exile until his death in 1943, sparked an inquiry with suspicions it was a German or Russian conspiracy but it turned out the pilot took the bomb aboard.
British Prime Minister Winston Churchill was dragged into the investigation as security chiefs scrambled to uncover the truth about what happened on the plane over the Atlantic, a year before Sikorski's death in a mysterious plane crash.
The pilot said he found a smoldering bomb on board the plane taking Sikorski from Scotland to Canada on March 21, 1942.
Polish Wing Commander Bohdan Kleczynski said he found the device burning under his mattress as he rested on the B-24 Liberator plane. He said the device broke into two pieces as he rushed to the back of the plane to throw it down the toilet.
"The detached part was so hot I threw it straight into the lavatory pan," Kleczynski told investigators, according to documents made public at Britain's National Archives.
Despite his seniority and reputation as one of Poland's finest fighter pilots, investigators quickly doubted his story.
Intelligence agent Lord Rothschild, who led the inquiry, said: "The story is fishy ... I am somewhat doubtful if this is a real attempt to liquidate the general."
Investigators questioned everyone on the plane and examined the small incendiary device. They found no evidence the bomb had partially exploded.
Other passengers said they too had smelt burning, but this had been traced to a minor electrical fault on the plane.
With the evidence stacking up against him, Kleczynski bowed to mounting pressure and finally admitted he had lied.
The bomb was his. The pilot always carried it with him in case he was shot down and needed to blow up his plane.
He had inadvertently taken the device onto the Polish leader's plane and panicked when he smelled burning during the flight, wrongly assuming the bomb was about to explode.
When told of the true nature of the "plot", Churchill wrote to Sikorski asking that the story be kept secret.
"He has been sufficiently punished by the mental anguish that he has passed through," Churchill wrote. "Having told one lie ... he was compelled to go on lying."
Sikorski died in a plane crash in Gibraltar a year later.
Debate still rages in Poland over what brought his plane down on July 4, 1943.
An inquiry failed to establish the cause of the accident, but ruled out sabotage. However, a second British investigation in 1969 said there might have been foul play.