Paul Simon learned the English traditional song ‘Scarborough Fair’ from Martin Carthy in the 1960s; he and Art Garfunkel recorded it and of course had a huge hit with it. It’s obvious when you listen to Carthy’s recorded version (which predates Simon’s) that Simon has based his arrangement on Carthy’s. By the way, this song is a descendent of an old song called ‘The Elfin Knight’, in which an elfin knight and a woman challenge each other to impossible tasks; you can find some of the early versions of this song in the Child Ballads here. More info at Mainly Norfolk here.
This recording is from Martin’s very first album, Martin Carthy, released in 1965. It is an excellent album and well worth getting.