The tune commonly used for it is also used for a widely sung hymn (and a good one, too, Lord of all hopefullness. It was written by "Jan Struther", real name Joyce Maxtone Graham, 1901-1953 - I don't know whether she put the tune to it or not; but I wonder whether it might have been a hymn tune already (for some previous hymn) even before it attached itself to the Banks of the Bann.