The song Nashe sings
is a song called "Jerusalem," which is based on a poem by William Blake:
http://en.wikipedia.org/wiki/And_did_those_feet_in_ancient_time.
It was also sung in The Loneliness of the Long Distance Runner (1962), among others.
For a little more on this, see http://www.imdb.com/title/tt0056194/board/flat/36277546
.