I've read "Flower of Scotland, Roy Williamson my Father" by Roy's daughter Karen. If I recall correctly there is a part somewhere in the book that details Roy learning to play the fiddle, which if Karen is correct he learned by ear with minimal help from others. Additionally the book states that fiddle was one of the last instruments he learned to play. That explains why you don't hear one in the earlier recordings. Ronnie's book doesn't mention fiddle at all and I don't think he can play it.