Intelligence officers could find no trace of the actor’s birth in Britain despite Chaplin always claiming he was born in London in 1889.
The mystery surrounding his origins emerged when the US authorities asked MI5 to look into the comic actor’s background after he left America in 1952 under a cloud of suspicion over his communist links.
But British officers could find no birth certificate and the earliest official record was a passport issued in 1920.
They investigated suggestions he was born in Fontainebleau, near Paris, or nearby Melun, while the Americans claimed his real name was Israel Thornstein and raised the idea he may have been a Russian Jew.
Despite extensive searches, MI5 could find no evidence of any of the claims leaving his true origins a mystery to this day.
However, British intelligence rejected American claims that Chaplin was a high-risk communist, concluding that while he may have been a “sympathiser” he was no more than a “progressive or radical”.
Agents here accepted his name had “been exploited in the interests of communism as one of the victims of ‘McCarthyism’ – the US anti-communist campaign led by Senator Joe McCarthy – but said he was not a security risk.
It is the first time the files kept by MI5 on Chaplin have been made public and show the extent to which agents went in checking his background.
The star said he was born on April 16 1889 in East Street, Walworth, south London – just four days before the birth of Adolf Hitler, whom he lampooned in his classic 1940 film The Great Dictator.
Files released by The National Archives in 2002 showed that the British Government blocked Chaplin’s knighthood for nearly 20 years because of US concern about his colourful private life and political affiliations.
He was eventually knighted in March 1975 and died at his home in Switzerland on Christmas Day 1977, aged 88.