The most popular theory surrounding the downing of BOAC Flight 777 is that German intelligence mistakenly believed Winston Churchill was on the flight.
This theory appeared in the press within days of the incident, and Churchill himself supported it.
In late May 1943, Churchill and Foreign Secretary Anthony Eden travelled to North Africa for a meeting with United States General Dwight D. Eisenhower.

The German government was eager to assassinate Churchill on his return flight home, and monitored flights in and out of the region in case the Prime Minister tried to sneak home aboard a civilian airliner.
This scenario was plausible as Churchill flew to Britain from Bermuda in January 1942 aboard a scheduled commercial airline flight.
Rumours had circulated since early May that Churchill might fly home from Lisbon.
Some have speculated that Britain's Secret Intelligence Service planted these rumours to mask Churchill's travel itinerary.

According to the Churchill assassination theory, as passengers were boarding BOAC Flight 777, German agents spotted what Churchill described in his memoirs as "a thick-set man smoking a cigar," whom they mistook for the Prime Minister.
This man was later identified as Alfred T. Chenhalls, Howard's accountant and portly travel companion.
In addition, some have speculated that the tall and thin Howard may have been mistaken for Detective Inspector Walter H. Thompson, Churchill's personal bodyguard who had a similar physical appearance.
There is an even more elaborate version of this theory that posits Chenhalls was employed by the British government as Churchill's "deliberate double" and that he and Howard boarded BOAC Flight 777 knowing they were going to die.
An alternative version of this is that the British government had intercepted German messages via the Ultra code breaking operations, but failed to notify the BOAC Flight 777 for fear of compromising the use of Ultra decrypted messages.
Both Flight 777 (1957), a book by Ian Colvin about the incident, and In Search of My Father (1981), by Leslie Howard's son Ronald Howard, lend credence to the idea that BOAC Flight 777 was downed because the Germans thought Churchill was on the flight.

Churchill appeared to accept this theory in his memoirs, although he is extremely critical of the poor German intelligence that led to the disaster.
He wrote, "The brutality of the Germans was only matched by the stupidity of their agents.
It is difficult to understand how anyone could imagine that with all the resources of Great Britain at my disposal I should have booked a passage in an unarmed and unescorted plane from Lisbon and flown home in broad daylight."
As it was, Churchill travelled back to Britain via Gibraltar, departing on the evening of 4 June 1943 in a converted Consolidated B-24 Liberator transport and arriving in Britain the next morning.

In the BBC television series, Churchill's Bodyguard (original broadcast 2006), it is suggested that (Abwehr) German intelligence agents were in contact with members of the merchant navy in Britain and were informed of Churchill's departure and route.
German spies watching the airfields of neutral countries may have mistaken Howard and his manager, as they boarded their aircraft, for Churchill and his bodyguard.
Churchill's Bodyguard noted that Thompson wrote that Winston Churchill at times seemed clairvoyant about suspected threats to his safety, and acting on a premonition, he changed his departure to the following day.
The crux of the theory posited that Churchill asked one of his men to tamper with an engine on his aircraft, giving him an excuse not to travel at that time.
Speculation by historians has also centred on whether the British code breakers had decrypted several top secret Enigma messages that detailed the assassination plan.
Churchill wanted to protect any information uncovered by the code breakers so the Oberkommando der Wehrmacht would not suspect that their Enigma machines were compromised.
Although the overwhelming majority of published documentation of the case repudiates this theory,
The most popular theory surrounding the downing of BOAC Flight 777 is that German intelligence mistakenly believed Winston Churchill was on the flight. This theory appeared in the press within days of the incident, and Churchill himself supported it. In late May 1943, Churchill and Foreign Secretary Anthony Eden travelled to North Africa for a meeting with United States General Dwight D. Eisenhower.
The German government was eager to assassinate Churchill on his return flight home, and monitored flights in and out of the region in case the Prime Minister tried to sneak home aboard a civilian airliner. This scenario was plausible as Churchill flew to Britain from Bermuda in January 1942 aboard a scheduled commercial airline flight. Rumours had circulated since early May that Churchill might fly home from Lisbon. Some have speculated that Britain's Secret Intelligence Service planted these rumours to mask Churchill's travel itinerary.
According to the Churchill assassination theory, as passengers were boarding BOAC Flight 777, German agents spotted what Churchill described in his memoirs as "a thick-set man smoking a cigar," whom they mistook for the Prime Minister. This man was later identified as Alfred T. Chenhalls, Howard's accountant and portly travel companion. In addition, some have speculated that the tall and thin Howard may have been mistaken for Detective Inspector Walter H. Thompson, Churchill's personal bodyguard who had a similar physical appearance. There is an even more elaborate version of this theory that posits Chenhalls was employed by the British government as Churchill's "deliberate double" and that he and Howard boarded BOAC Flight 777 knowing they were going to die. An alternative version of this is that the British government had intercepted German messages via the Ultra code breaking operations, but failed to notify the BOAC Flight 777 for fear of compromising the use of Ultra decrypted messages. Both Flight 777 (1957), a book by Ian Colvin about the incident, and In Search of My Father (1981), by Leslie Howard's son Ronald Howard, lend credence to the idea that BOAC Flight 777 was downed because the Germans thought Churchill was on the flight.
Churchill appeared to accept this theory in his memoirs, although he is extremely critical of the poor German intelligence that led to the disaster. He wrote, "The brutality of the Germans was only matched by the stupidity of their agents. It is difficult to understand how anyone could imagine that with all the resources of Great Britain at my disposal I should have booked a passage in an unarmed and unescorted plane from Lisbon and flown home in broad daylight." As it was, Churchill travelled back to Britain via Gibraltar, departing on the evening of 4 June 1943 in a converted Consolidated B-24 Liberator transport and arriving in Britain the next morning.
In the BBC television series, Churchill's Bodyguard (original broadcast 2006), it is suggested that (Abwehr) German intelligence agents were in contact with members of the merchant navy in Britain and were informed of Churchill's departure and route. German spies watching the airfields of neutral countries may have mistaken Howard and his manager, as they boarded their aircraft, for Churchill and his bodyguard. Churchill's Bodyguard noted that Thompson wrote that Winston Churchill at times seemed clairvoyant about suspected threats to his safety, and acting on a premonition, he changed his departure to the following day. The crux of the theory posited that Churchill asked one of his men to tamper with an engine on his aircraft, giving him an excuse not to travel at that time. Speculation by historians has also centred on whether the British code breakers had decrypted several top secret Enigma messages that detailed the assassination plan. Churchill wanted to protect any information uncovered by the code breakers so the Oberkommando der Wehrmacht would not suspect that their Enigma machines were compromised. Although the overwhelming majority of published documentation of the case repudiates this theory, 
BOAC Flight 777