Maud,
I'm sure the Sweethearts name is more widespread than that - I know it from Gloucestershire - but the indispensible The Englishman's Flora by Geoffrey Grigson only lists it as from Somerset, but then language research moves on, and the book is 45 years old.
He quotes the Flora Vectensis (1856) as saying that it was commonly chopped up and fed to young goslings in the Isle of Wight. It is recorded in an old herbal as a cure for skin diseases, scurvy and piles, although what the exact treatment might have been in the latter case I don't know.
Joe