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.
The song "Look for a Star" became a hit for Gary Mills. Buzz Cason recorded the song using the pseudonym Gary Miles. "Look for a Star" is credited to composer Mark Anthony, a pseudonym for Tony Hatch, famous for writing "Downtown" for Petula Clark.
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
Tony Hatch originally wrote the theme song for "Follow a Star (1959)," but it wasn't used. Hatch changed the title to "Look For A Star."