Following the advice of @Gordon Shumway I have searched for and found a public domain PDF of volume five of Cecil Sharp's "Folk Songs of England", which features top line and piano for 15 Sussex folk songs collected by W. P. Merrick; the first 14 songs have accompaniments written by RVW. Here is a link to the collection of all five volumes: https://imslp.org/wiki/Folk-So.....%2C_Cecil)
 - These volumes are not public domain in EU, and likely not in US. The collection is hosted in Canada, where the copyright extends to only life +50 years.
This represents a good starting point for my extended search, and so thank you all for your advice.
With best wishes,
"It is vain to do with more that which can be done with less" - William of Ockham
"A crown is merely a hat that lets the rain in" - Frederick the Great
To my surprise, I found this book on my shelves last night. I've never really opened it.
It is what it says - songs from the Southern Appalachians, but supposedly imported there from Britain by 18th c. settlers and passed on orally.