Donald Gray

as The Mysterons / Colonel White / Captain Black (voice)

as Captain White / Captain Black / The Mysterons (voice)

as Colonel White / Captain Black / The Mysterons (voice)

as Father Conrad

as Sir John Brinder

as The Mysterons / Colonel White / Captain Black (voice)

as Polly's Husband (uncredited)

as Inspector Wills

as Extra (uncredited)

as Captain Ross

as Headmaster

as Col. George Gordon

as Robert Maitland

as TV Program Announcer (uncredited)

as Paul Merton

as Jimmy Thompson

as William Peck

as Peter Burroughs

as Young Yacht Guest (uncredited)

as Don (as Eldred Tidbury) (uncredited)