had long noted the similarity of the Twa Corbies melody and a popular Breton folkdance tune. But I thought the tune went far back in the history of British folkmusic. How disillusioned I am to be told that Steeleye Span borrowed the Breton tune to set the Twa Corbies lyrics to. I was looking conformation of that attribution and I see from this thread that Jean Redpath recorded the Twa Corbies with Breton air before Steeleye Span, and that Jim McLean says that "Morris Blythman AKA Thurso Berwick set The Twa Corbies to the Breton tune Al Alarc'h sometime in the fifties." In another Mudcat thread, Malcolm Douglas wrote in Apr 2000 that the song was set to Al Alarch'h in the 1960s and that there are different opinions as to who set the lyrics to that tune.

https://folkhistory.blogspot.com/2013/11/twa-corbies-as-deconstructionist-ballad.html

The author suggests that the Twa Corbies was composed as a parody of or rebuttal of the sentimentality of The Two Ravens ballad.