On 30 October 1938, with a clear announcement that this was a programme by ‘The Mercury Theatre on the air’, Orson Welles and his talented team broadcast one of the most famous hours of radio entertainment in media history.

His adaptation of HG Wells’s War of the Worlds junked all the conventions of the play and instead presented the Martian invasion as if it was really happening, with all the chaos of a live news report.

The result was a sensation, with people who’d tuned in late phoning the authorities in hysterics and the newspapers the next day accusing Orson of a grand hoax.

It was nothing of the sort, though it was a great stunt, and as this evocative documentary makes clear, a brilliant one-off.