This is a Child ballad, well documented in the usual places, e.g...

Wikipedia: The Lochmaben Harper
Child: Google Books
Bronson: Google Books
Mainly Norfolk: Lochmaben Harper / The Blind Harper / The Wanton Brown
Roud: Roud no. 85

I too first heard it from the singing of Nic Jones, in or around 1973. He sang it on the John Peel (radio) show as well, of which I have but a fragment on tape (last couple of verses only, late with switching on the recorder!). Nic's arrangement is very nimble and appealing!

- Tony