Not THE tune, Bryn, just A tune... Mark Dowding's research dug up the original tune written by C. Coote jr. to Harry Clifton's words...

Now I'm a bit of a stick-in-the-mud (shurrup, Mark!), and tend to prefer the first tune I've learned to a song... but the original tune for Calico is far better than the more well-known one by a long chalk. It has a bounce that brings the lyrics to life.