Even in 1952, with the best years of his movie career behind him, Charlie Chaplin had one of the biggest names in Hollywood. But according to newly released MI5 files the authorities were not convinced it was really his: asked by a suspicious US to investigate Chaplin's early years in England, British intelligence officers were unable to locate the star's birth records.

Though he was believed to have been born in Walworth, in south London, on 16 April 1889, no birth certificate could be found in files at Somerset House, leading MI5 to conclude Chaplin "was either not born in this country or that his name at birth was other than those mentioned". A hunt for references to "Israel Thornstein" – a possible alias, or so claimed the US – also proved fruitless. And when a source suggested to Scotland Yard's Special Branch that the actor may have been born near Paris, the foreign intelligence service, MI6, was sent to search in vain for evidence.

The US government's interest in Chaplin – a resident since 1912, though never an American citizen – stemmed from his supposed Communist sympathies. In an era of McCarthyist witch-hunts, Chaplin was privately disparaged by the FBI director J Edgar Hoover as "one of Hollywood's parlour Bolsheviks". When the star sailed for Britain in 1952 to attend the premiere of his new film, Limelight, Hoover was determined to find grounds on which to deny him re-entry.

In communications with British intelligence, released today by the National Archives in Kew, the Americans asked their transatlantic counterparts to trace the actor's old passports, hoping for evidence of visits to the USSR. All to no avail. "US government cannot prove party membership," ran a telegram from Washington, copied to MI5's then director-general, Sir Percy Sillitoe. If all else failed, the message went on, details of Chaplin's personal life could be brought to bear: "He has been involved in paternity and abortion cases. Being an alien, Immigration can exclude him for moral turpitude."

When the US Attorney General, James McGranery, announced he would indeed revoke the actor's re-entry permit, Chaplin settled in Switzerland. In 1958, when it was reported the US was still pursuing him for $500,000 (£315,000) in unpaid taxes, he described his treatment as "revengeful and continual persecution". He would not return to America until 1972.

Due to US objections, Chaplin was denied a knighthood until 1975, but the British remained unmoved by allegations about his politics. When he took a holiday in Kenya in 1958, for example, a message to MI5's East Africa liaison officer denied he was a security risk: "It may be that Chaplin is a Communist sympathiser, but... he would appear to be no more than a 'progressive' or radical."