Sorcha - From the initial description I suspect this is a song like "The Ballad of St. Anne's Reel" that makes reference to a well-known fiddle tune, but is not the tune itself. "The Ballad of St. Anne's Reel" uses the melody of the fiddle tune as instrumental breaks between verses - but the verses are sung to a different melody.

That said, I wonder if this song about "Mason's Apron" uses the fiddle tune melody in any way??   

Sorry, I don't know the words to it, look forward to seeing them.