I have always assumed (no evidence, just a hunch) that the Anthem was originally composed for a pageant. These were very popular as village or town celebrations in the 1920s and 30s, with everyone dressing up in costume and re-enacting bits of local history or legend. I imagine that there would be appropriate music, dance or song wherever there was enough talent to provide it.

A march-past of a squad of DCLI players would probably not be out of place in Cadgwith, especially if local men had served on the NW frontier (and told their stories endlessly at the pub for years after), and a short song with a highly singable chorus would be just the thing as they took the salute.

I have came across a couple of other pieces that I feel could have their origins in 20th cent pageants or civic ceremonies (might make an interesting thread). One is "William Rufus", another "Sir Sidney Smith's March".