Thank you to Lighter for the information. "Sweet Evelina" does seem to be the origin of the song I heard, but after 150 years of oral transmission, it has changed quite a bit. I listened to a rendering of "Sweet Evelina" on YouTube and the tune is fairly similar to the version I got. So in the absence of any other information, we'll call that a result. I wonder what path it took from a cowboy song to rural Gloucestershire? We'll never know.

Tradsinger