Three Guitars Mood 2

"Three Guitars Mood 2" was an instrumental song by John Smith and the Common Men, favoured by Susan Foreman. She played the song and danced to it the day she was forced to leave 1963 London with her grandfather and her two schoolteachers Ian Chesterton and Barbara Wright. Ian made her turn it off due to his "very sensitive ear". (TV: "An Unearthly Child")

Behind the scenes
The song is not named in the episode. In the real world, it's called "Three Guitars Mood 2", and was actually written by Nelson & Raymond/The Arthur Nelson Group — not the Common Men.

The song had been previously heard nearly two years earlier on 2 January 1962, in the  episode "". The song was released on the Doctor Who Appreciation Society cassette Space Adventures - Music from Doctor Who 1963-1968 in 1987.