Late British actor Sir Michael Redgrave was investigated by the British secret service for 20 years, according to newly-released official files.

Redgrave, who died from Parkinson's disease in 1985 aged 77, had a career spanning almost 40 years and starred in more than 50 films, including acclaimed war drama The Dam Busters.

It has now emerged that Mi5 officers kept tabs on Redgrave during the height of the Cold War because they suspected him of being a Communist sympathiser.

The actor first came to the agency's attention in 1940 when he signed a Communist inspired manifesto and over the next nine years, they detailed 21 occasions in which he aroused suspicion of left-leaning views, including numerous trips to Russia.

The 105-page document on Redgrave is among a number of official files which have been released by Britain's National Archives. The file also contains notes on Redgrave's wife Rachel, who was also monitored by the spy network, as well as his actor offspring, Vanessa, Corin and Lynn.