According to the sleeve notes of "Bundook Ballads", MacColl's source was Harry Cox:

THE TROOPER CUT DOWN IN HIS PRIME
This ballad is probably the oldest of British barrack-room favourites. It exists in many variants, and is a standard song among all 'sweats'. Veterans of World War I claim that the song originated in the first expeditionary force in France, but, of course, it is very much older, tracing back to the eighteenth century street ballad, The Unfortunate Rake. I recently heard a ninety year old actor, Norman Patridge, sing a version which he said was current with troops in the Boer War, and which varied hardly at all from the version included in this album, which was learned from Harry Cox, traditional singer from Norfolk.