Ed Bishop replaced Peter Dyneley, after rushes revealed the latter's physical similarity to Patrick Wymark, which was thought likely to confuse audiences.
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.
Lynn Loring, real-life wife of Roy Thinnes replaced Tisha Sterling, who had to withdraw because of illness.
Many of the sets, costumes and vehicles (and even some of the cast members) were reused in Gerry Anderson's TV series UFO.
The Phoenix spacecraft's power reactor is depicted as having been manufactured by Rolls Royce.