This was originally planned as a Carl Foreman production, and he may have done a version of the screenplay (there are characters named Weaver and Grogan in the film - a trademark of Foreman's) before hiring Bryan Forbes to write the film as a planned vehicle for Cary Grant. When Forbes presented his version, Foreman said it was not good enough to present to a star of Grant's magnitude, and the project went into abeyance for a while. When Forbes formed Allied Film Makers with Michael Relph, Basil Dearden, Richard Attenborough and Jack Hawkins, they obtained the necessary rights and made the film themselves - it was a great critical and financial success.
A notable early portrayal of gay characters, although mostly heavily hinted at. The actors at the theatre are extremely camp, and one of the bank robbers appears to have left the army possibly due to his sexuality.
In John Boland's original novel, the robbers are inspired by a novel about a robbery - a real novel, Lionel White's "Clean Break". This book was the basis for Stanley Kubrick's film, The Killing (1956). Bryan Forbes retained this idea in his screenplay, but made the novel an invented one with a different title ("The Golden Fleece") with its authorship credited to a certain "John Seaton" - a pseudonym Forbes himself had used in his days as a feature-writer on the British fan magazine "Picturegoer". He used this name again for the writer character played by Christopher Plummer in International Velvet (1978), which Forbes also directed.
The army camp that the League Of Gentlemen raid was built around the now disused Timekeepers Entrance at Pinewood Studios. In some low angle shots, the famous water tower can be seen clearly in the background. This entrance was utilized in many films from that period, including another barracks entrance in Guns at Batasi (1964), a research lab in Carry on Spying (1964) and Elsbels Airport in Carry on Abroad (1972). Since the construction of the new entrance, the Timekeepers (which was the main entrance into the studio) has been sealed off.