Teribus - the 'coats of red' verse was added much later by Billy Ross, once of Ossian - see his message above.

It would have been written sometime between 1976 and 1982, I imagine, so it's not going to help us determine the origin of the song.

Even though the song pre-dates the First World War, that does not mean that it has nothing whatsoever to do with the First World War.