I think it was a Runrig song used by Carlsberg. A friend of mine was most annoyed by the fact. I seem to recall "She moved through the fair" being used for Irish beer once. Then wasn't the tune for "Country Life" butter a trad melody?

I don't have a problem with it being used as long as it isn't just being used to take the piss out of folkies. If the music is being used for effect and it creates a positive effect which attracts people to the music then fair play.