I had intended to post the following when this song was last discussed, but seem to have forgotten. Here it is now.

What is interesting is how a pretty, but not particularly distinguished piece of commercial songwriting made in a regular, almost march-like 4/4 time evolved, in the repertoire of the Copper family of Rottingdean, into a proper folksong of genuine beauty. The
Coppers, of course, have a family singing tradition going back many generations; with them, the song lost its rather dogged rhythm and
adopted a mixed 5/4, 6/4 and 3/2 time typical of the English folk style of the 19th century; the melody developed, too, gaining subtlety in the process; this would be not unrelated to their practice, relatively unusual in recorded English tradition, of singing in harmonies of several parts. Compare the original as published by Jefferys and Nelson with the Coppers' version of it and you'll see what I mean.

Once the Folk Revival of the 1950s and later was up and running, various Revival performers took the song up; Nic Jones began to sing it, and Mary Black later learnt it from him and recorded it. Her arrangement of the Coppers' version was governed by quite different
sensibilities, and the demands of a conventional accompaniment forced the song back into a more regular, less free rhythm; it was already
well on the way to becoming a Country and Western piece. People who have recorded it subsequently seem mainly to have learnt it from
her record, and are often unaware of its antecedents (sometimes imagining it to be in some way Irish) and of how much they owe to the Coppers for turning a bit of brass into something a little more like gold.

Here is a midi I made earlier(!) from the sheet music at Levy. I've included the full piano accompaniment which, I think, rather reinforces my point.

The Rose of Allendale: original arrangement.