BRITISH spies investigated documentary TV series World in Action to root out any communist influence among its staff, a “top secret” file declassified today reveals.

The sinister operation by MI5 has remained under wraps for over half a century and was buried in a Cabinet Office cache of “ultra-sensitive stuff that was too hot to handle at the time,” according to a top historian.

The file shows that, as early as 1962, Whitehall’s official committee on communism conducted a study that found: “No evidence to suggest that Independent Television programmes were unduly slanted towards communism or that the companies were excessively open to communist penetration.”