This is all over the place. It seems derivative of Harry Bates' short story from 1940 "Farewell to the Master" as an alien - in this case from Venus - arrives to tell humanity to ditch nuclear weapons. Patricia Neal seems to pretty much reprise her role from "The Day The Earth Stood Still" (also based on the same short story) as she and Cyril Luckham try to engage with our alien visitor, played by an almost static Helmut Dantine. He has landed in the UK but the radio announcements reporting his arrival all have American accents (not very BBC) and the special effects, such as they are, are pretty basic. Burt Balaban may have devised his direction to have a somnambulant effect - this is a very, very slow burn. It does contain the great quote "I can find no pulse, therefore there are two possible explanations: either I am drunk, or you are dead"