The song "Look for a Star" became a hit for Garry Mills in Great Britain, and for Garry Miles in the United States. Tony Hatch wrote it under his regular pseudonym, Mark Anthony.
Much of the action was filmed at Billy Smart's Circus, one of the three "big tent" circuses in the United Kingdom at the time. The external scenes were filmed on Clapham Common. The boards on the ringside seats have BS painted on them. Presumably, Anton Diffring's character has the same initials to save the expense of replacing the boards.
In one scene, the clowns are dressed as Keystone Cops.
Much of the British Billy Smart circus seen here was used again in the 1967 horror movie, Berserk, staring Joan Crawford , where performers were also being murdered, but for a very different reason