Secrets of Scotland Yard

Secrets of Scotland Yard is a 1944 American thriller film directed by George Blair and starring Edgar Barrier, Stephanie Bachelor and C. Aubrey Smith. The screenplay was by Denison Clift, adapting one of his own stories Room 40, O.B. from Blue Book Magazine. A British police detective goes undercover to root out a Nazi spy in Britains decoding organization.

Source: Wikipedia