Several web sites mention a song called CALLERS, words by Caryl Brahms, music by Arthur Benjamin. Sheet music "for unison voices and piano" was published by Boosey & Hawkes, 1949.

The words to CALLERS were apparently taken from a book "The Moon on My Left" by Caryl Brahms (London: V. Gollancz, 1930), 84 pages, classified as "Fiction, Juvenile audience."

However, I have been unable to find any quotes from the song, so I am unable to confirm that it's the right song.