I'm going on memory here, gang, but Dear Old Percy did not write the tune for "Mountains of Mourne". As best I recall, he literally wrote the lyric on the back of an envelope and sent it to his some-time collaborator (Charles Collison, or something similar) who then fitted the lyric to an existing air. I'll check back on the weekend, and if nobody else has confirmed my recollection, I'll try to dig up some documentation.