Gerry Anderson has said in interviews that he had to shoot all the important stuff with Patrick Wymark and Ian Hendry in the mornings because both men well known for being heavy drinkers of the booze would go for liquid lunches and would not be able to do much in the afternoons.

Many of the sets, costumes and vehicles (and even some of the cast members) were reused in Gerry Anderson's TV series UFO (1970).

Lynn Loring, real-life wife of Roy Thinnes replaced Tisha Sterling, who had to withdraw because of illness.

Ed Bishop replaced Peter Dyneley, after rushes revealed the latter's physical similarity to Patrick Wymark, which was thought likely to confuse audiences.

The Phoenix spacecraft's power reactor is depicted as having been manufactured by Rolls Royce.

Patrick Wymark's character complains of heart trouble early in the film. Ironically, Wymark really did have a bad heart and died the following year.

The cardiometer wrist watches that several of the characters wear correctly predicted the widespread use of fitness-watches nearly 40 years after the movie was released.

All of the computer sound effects are actually the sounds of a Strowger telephone exchange.