Buster Keaton was originally considered for the lead, but the backers of the film refused to support the project with him as the star. John Mills was then cast but suffered a broken leg and the project was postponed until many years later in 1973.
After Keaton, John Mills and then Danny Kaye were considered for the central role before Peter Sellers expressed an interest in the project.
Donna Mullane and John Chaffey gave up acting soon after this film. In a 2023 interview with 'Best of British' magazine, John said he wasn't really interested in continuing acting anyway as he wanted to have a normal schooling and he said Donna's family didn't seem keen on her pursuing an acting career and probably talked her into giving it up. He also said he hasn't heard from her since the premiere and has no idea where she is.