Thanks everybody!

Anglo,I very much envy your knowledge on Breton matters ;)

It would have been fascinating if actually the ballad's marriage with the tune belonged to scottish or irish folk tradition since a LONG time before it actually does,as I thought in the beginning...It would have meant the survival of a tune through a huge slice of history in wich Breton celts and Britain celts went separate ways...ok,there goes the dreamer.
But if anyone can come up with a tune or some folk subjects that can be found in both breton tradition and scottish/irish/welsh tradition,I'd be SO interested...

(It makes me think:how old can a tune be,how long can a musical traditon last?!)(maybe I should start a thread about it...)