Apologies; aspects of my contribution above are misleading.

This is generally associated with versions of Child 77 Sweet William and Lady Margaret.

However, in this form, it appears to be confined to north Ulster.

Len Graham, Jimmy McBride and Hugh Shields found it among Donegal singers. Len Graham found two other people who sang it, one of whom I know came from North Antrim, I have no knowledge of the location of the other.

It seems fairly certain that the impulse for all these versions was the ballad sheet I mentioned