Was the great comedian Charlie Chaplin secretly Jewish? His mixture of pathos and humour had a Jewish "feel" and fans were all too ready to believe that his real name was Israel Thornstein.

This was the alias he was given by the FBI and MI6 in secret papers released by the National Archive this week.

They show how Chaplin was under surveillance by security men during the feverish anti-Communist atmosphere in Washington and London during the 1950s.

Top of their list, they said, was to discover the star's real identity. Although he was born in Kennington in 1889, (his mother, Hannah, was a musical comedy actress), a Special Branch officer wrote to MI5 that there was evidence that he had been born in France.

They added that there was no sign of a "Chaplin" being born in London in 1889. There was also no evidence about the actor's original name, although according to some US sources, including a 1948 Jewish encyclopedia, he was known to be Israel Thornstein.

Intelligence reports about the star were headed: "Charles Chaplin/alias Israel Thornstein". In addition he was said by Special Branch to be "of Jewish German origin."

Both MI6 and a senior American embassy official exchanged notes that said Chaplin had been an active member of the Communist Party and supported the Soviet Union during the war.

To the end of his life, there were those who described him as Jewish. Mainly antisemitic websites still cite the name Israel Thornstein as "proof" of his origins. The conspiracy theories were buttressed by Chaplin's bitter attack on the Nazis in his film, The Great Dictator.

Chaplin always refused to deny the claims, saying that to do so was to play into the hands of the antisemites.

As for the FBI, they kept the file on Chaplin's left-wing connections open until his death in 1977.