On screen he portrayed British military heroes such as Henry V, Lord Nelson and the Duke of Wellington.

In real life Laurence Olivier performed some bravery of his own, risking imprisonment and even assassination as an agent for Britain.

The celebrated actor, mistakenly accused by some of his contemporaries of lacking patriotism for deciding to remain in Hollywood when war broke out rather than return home and sign up, worked secretly to help secure the hearts and minds of a sceptical America during the early stages of the Second World War, it has been revealed.