Hi Brian,
You asked specifically about U.K. source singers, but if you want to broaden your query to include U.S. tradition-bearers, you might want to be in touch with Jean Ritchie (you can PM her under her Mudcat name, Kytrad). She grew up in a family of traditional singers in Kentucky and, as you know, went on to make a major place for herself in the folk revival. If you haven't yet had this conversation with Jean, she would be a great person for you to chat with about what she herself has done with some of her many traditional family songs.
Kathy