According to John Heseltine, who restored the car for the film, star David Niven couldn't master the idiosyncratic gearbox of the white 1937 Cord 812 Supercharged Phaeton Convertible, and subsequently it was driven in bottom gear, resulting in it overheating. The scene in the film showing the steaming Cord was hastily rewritten to work around the problem. The car had to be restored from nothing but a rusty collection of parts in just six months to get it ready for filming.
Cast and crew who worked on both this movie and the following year's Casino Royale (1967) included star David Niven, actors Robert Rietty, Geoffrey Bayldon, and John Le Mesurier, producer Val Guest, screenwriter Wolf Mankowitz, art director John Howell, editor Bill Lenny, and sound technician Jim Shields.
The Metro-Goldwyn-Mayer (MGM) film studio intended to make a series of secret agent Jason Love movies. David Niven and producer/director Val Guest had even taken out an option on the film rights to the next five "Jason Love" books by James Leasor, but they were never produced.
The make and model of Dr. Jason Love (David Niven)'s vintage sports car that he drove was a white convertible 1937 Cord convertible coupe, supercharged. In excellent condition an example of this auto could be worth upwards of $350,000 or more. The make and model of the car that Love was promised for completing the spy mission was a 1936 Cord 810 prototype with body by LeBaron. Only about 5 or 6 of these were made.
The film was extensively re-edited in Hollywood under the supervision of veteran editor Margaret Booth, whose contributions were not credited. These changes (which led to the prominently-billed Cyril Cusack having only a minute or so of screen-time) were made against the wishes of director Val Guest.