Well, I've written a tune for it now. Not sure how I can write it down as I don't know ABC notation. As befits a traditional song like this one, the tune's similar to a lot of other tunes, but I hope not quite the same as any of them. (But knowing my luck, there will be some b*gg*r who recognises it as a tune I hadn't heard, and say I copied it from a "real" traditional tune.)