From a post on QRP-L:
This is a 30-minute BBC documentary called “Wartime Radio: The Secret Listeners” made in 1979. Its about how ham radio operators set up the first intelligence gathering listening posts in WW1 and WW2. Pretty cool stuff that I’d never heard of. All they had then was cw and the UK govt recruited hams to be Voluntary Interceptors.
from the site:
“Illustrated with archival film and photographs, as well as interviews with those involved, the documentary traces the evolution of civilian involvement in radio-based intelligence during both world wars.”