UFO is about the ongoing covert efforts of a government defence organisation to prevent an alien invasion of Earth.
A single series of 26 episodes was filmed over the course of more than a year; a five-month production break was caused by the closure of
MGM-British Studios in Borehamwood, where the show was initially made. Production then moved to Pinewood Studios in Buckinghamshire.
UFO was first broadcast in the UK and Canada in 1970, and in US syndication over the next two years.
The Andersons’ live-action science fiction movie Doppelgänger (also known as Journey to the Far Side of the Sun) is considered an immediate precursor to UFO, which was their first entirely live-action TV series.
The series featured actors, costumes, props, locations and music that had appeared in Doppelgänger, and 11 cast members of the film appeared in at least one episode of UFO.
Following syndication in the US and initial favourable ratings, a possible second series was planned; initially entitled UFO 1999, this eventually became Space: 1999.