Correction to my first link above; should have been this:
http://www.concertina.info/carols/
There, the lyrics can be found on this page:
http://www.concertina.info/carols/files/words/nailsbourne_beasties_song.doc

Unfortunately, due to spam attacks, the folks who run the concertina.info site and host the Bradford on Avon Carollers pages are not electronically reachable through that site. Can someone pass word to Chris Timson, Anne Gregson or anyone else involved with the carollers that I'd like to get the tune for this song? Or can you furnish (by PM!) their working email address?