The Archers (Michael Powell and Emeric Pressburger's production company) weren't given permission to film inside Canterbury Cathedral. In any case, the stained-glass windows had been taken out because of the air raids, the aisles were filled with sandbags and earth to fight fires and to provide a soft landing for any masonry or sculptures that fell there. So the interior of the Cathedral was rebuilt in Denham Studio. They recreated it so well that Cathedral guides have been heard telling people that the film was shot in there.
John Sweet was not a professional actor, but a real-life army sergeant stationed with the American forces in wartime England. He donated his salary from the film to the NAACP. This was his only feature film role; he died in 2011, at age 95.
When Peter enters the cathedral he looks up towards the roof. That is the only shot that was taken inside the real cathedral. Despite not getting permission to film in there, the production sneaked that one shot with a hand-held camera.
On September 19, 2007, this film became the first ever to be projected to an audience in Canterbury Cathedral and was shown as a fund-raising event to pay for repairs to the cathedral caused by WW2 bomb damage.
"Gone with the Wind (1939)" author Margaret Mitchell was on her way to see a showing of this film with her husband when she was hit by a speeding car. She was knocked out, and died five days later, having never recovered consciousness.