Peter Lyncort (Glenn Ford) is mentioned as having been born in Quebec, Canada. Ford actually was born in Quebec.
Despite the fact that the film is set in 1950s Birmingham, there's not a trace of a Brummie accent from a single character. The cast managed "educated RP" cockney and estuary English - all from London and the southeast of England.
Final film of Arthur Hambling. NOTE: He died before the film's release. He played the role of "Train Driver".
Three years earlier in Ultimatum (1950), Victor Maddern had played the role of the soldier who shoots the mad bomber. However here, in a reversal of sorts, Maddern plays the part of the mad bomber.
Filmed on location including the MGM Studios in Boreham Wood, Elstree, England, and the railway line between Walsall and Wolverhampton, England, UK.