After the German invasion of Poland, which led to the outbreak of World War II, General Wladyslaw Sikorski became prime minister of the Polish government in exile. Working from London, he commanded troops and ran a formidable military intelligence.
General Sikorski ran the Polish war effort from London
Secret service papers - released for the first time by the National Archives in Kew, London - reveal claims of an attempt on his life in 1942.
On 21 March, General Sikorski, six of his staff - including Wing Commander Bohdan Kleczynski - and other crew members set off from Prestwick in Scotland on a Liberator aeroplane bound for Montreal.
As far as the general and others on board were concerned, the flight passed off without incident.
But a week later, after travelling on from Canada to the US, Wing Cdr Kleczynski gave to the FBI a chilling account of an attempt to blow up the plane.
He told officials in Washington that he had been travelling in the separate tail compartment of the plane, lying on mattresses spread on the floor, when he smelt burning rubber.
"Fearing a short circuit in the electricity cables I began to look under the mattresses for the source of any fire there might be," he said in his statement.
"When I slipped my hand below the mattresses, I felt a strong sensation of heat and drew out a very hot incendiary bomb. There was a 'cap' on the bomb that was heated to such a degree that the insulating tape was smoking."
Wing Cdr Kleczynski said that, in a panic-stricken state, he broke off the wire connecting the cap to the bomb and threw the cap into the plane's toilet.
Unsure if the bomb had been "rendered harmless", he said he sat on his own with the bomb for more than an hour until it had "cooled down completely".
"I put the bomb in my pocket and only reported the incident to you when we landed," he said.
It was not until 7 April that the British security service heard about the incident.
An inquiry headed by Lord Rothschild - in close liaison with Director General Sir David Petrie - was immediately launched.
From his first report into the incident, Lord Rothschild was sceptical about what he described as Wing Cdr Kleczynski's "fishy" account.
He suggested it was "almost inconceivable" the Pole had not reported an attempt to destroy the general's aeroplane until a week later.
Serious aspersions were also cast on the Polish wing commander's character.
In one report, Sir David said Wing Cdr Kleczynski was "a dope fiend, suffered from hallucinations, and was a pathological exhibitionist".
In June, Wing Cdr Kleczynski was called back to the UK from the US for questioning but he stuck to his original story.
Gen Sikorski was killed in a plane crash in July 1943
In a new statement, made on 27 June, he said he had not reported the incident immediately because "I did not want myself to say anything which might cause panic".
But, upon arrival in Washington, he had decided to speak up and had handed the bomb into the Polish Embassy before being questioned by the FBI, he said.
Lord Rothschild ordered an interrogation.
On 18 July - two days before that interrogation - a statement was taken from a British soldier who said that, when stationed in Fifeshire with Wing Cdr Kleczynski the previous December, he had given the Pole a small incendiary device "as a souvenir".
When this was put to Wing Cdr Kleczynski in his interrogation of 20 July, he eventually admitted being given the incendiary bomb. With this, the floodgates of confession had opened.
In his statement of confession, Wing Cdr Kleczynski said he had carried the bomb onto the flight, hiding it in his gas mask - which he put by his mattress - and then "more or less forgot about it".
He then smelt burning rubber and "at once thought that the bomb was about to go off," he said.
"I took the bomb out of the gas mask and went to the lavatory to throw it in. The bomb was warm and that also made me think it was about to go off.
"I am afraid I completely lost my head. Having the bomb in my possession and being in the plane with Gen Sikorski, I felt I was bound to get into serious trouble.
"I was afraid someone had seen me with it and, as I had been in the lavatory a long time - long enough for the bomb to get cool - I had to find some explanation, so I invented the story of finding the bomb on the plane.
"I told [the story to] another Polish officer on board."
Winston Churchill called for Wing Cdr Kleczynski to return to duty
Some days after the flight, his confidant had advised Wing Cdr Kleczynski to tell the authorities, which he did in Washington.
"They forced me to tell the story again and then I knew I should have to insist that the story was a true one," Wing Cdr Kleczynski said.
"I can only say that I do not know why I did it, except that I must have completely lost my head."
Perhaps surprisingly, after his constant criticism of Wing Cdr Kleczynski throughout the inquiry, Lord Rothschild - bringing the files on the incident to a close - said the Pole had "created a very favourable impression on me".
He also wrote to Prime Minister Winston Churchill, who was urged to contact Gen Sikorski to say that Wing Cdr Kleczynski be allowed to return to his duties.