Knock , Knock Who 's There ? " is a song written and composed by John Carter and Geoff Stephens . It was originally sung and recorded by the Welsh singer Mary Hopkin and was the United Kingdom 's entry at the Eurovision Song Contest 1970 where it came second . The single version was produced by Mickie Most and reached No. 2 on the UK charts . On 7 March 1970 , Mary Hopkin sang six songs at the UK National Final , '' A Song for Europe '' , which was aired on the television series '' It 's Cliff Richard ! '' . Hopkin was chosen by the BBC to be the United Kingdom 's representative for that year , and the winner of a postal vote would determine which of the six songs would progress with her to the finals in Amsterdam . " Knock , Knock Who 's There ? " , the sixth and final song performed that evening , won the postal vote with over 120,000 supporters
Eurovision Song Contest 1970
Eurovision Song Contest 1970
Knock, Knock Who's There?