GUEST above was me.

For ballad tunes in the British tradition, the most extensive work in this area was by S.P. Bayard, who classified all the Child ballad tunes (those later anthologized by Bronson) into 56 "tune families" which he thought were genetically related. (References in Bronson, "The Traditional Tunes of the Child Ballads", which you will need for this sort of study and which you can buy from CAMSCO). He got the idea from Bartok and his associates in Hungarian musicology; if you listen to enough Hungarian songs it's fairly obvious that they don't really have an individual identity, they sort of blur into each other.

https://en.wikipedia.org/wiki/Samuel_Preston_Bayard