According to the notes on the Corries album 'Kishmul's Galley' (1968), "A fragment of this song was collected by Hamish Henderson aboard the Irish ferry on numerous new year journeys. He only heard one fragment of the song and composed the major part of the song and tune himself."
Alas, I haven't got the lyrics written down but will try to do so over the weeked, unless someone beats me to it.