This song was written by John Carter and Geoff Stephens. It was recorded by Mary Hopkin in 1970 and was produced by Mickie Most. It was released as a single on the Apple Records label in 1970 with I’m Going To Fall In Love Again on the B-side. The single reached number two on the UK Singles chart. Knock, Knock Who’s There was the UK’s entry at the Eurovision Song Contest 1970 where it came second.