Here's a page with the song, and some stuff about Parson Hawker.

He seems to have been a quirky sort of man: "His eccentricity was a by-word. He dressed in claret-coloured coat, blue fisherman's jersey, long sea-boots and pink brimless hat. He talked to birds, invited his nine cats into church, and excommunicated one of them when it caught a mouse on a Sunday."

Here is what he wrote about the song:
The history of that Ballad is suggestive of my whole life. I published it first anonymously in a Plymouth Paper. Everybody liked it. It, not myself, became popular. I was unnoted and unknown. It was seen by Mr Davies Gilbert, President of the Society of Antiquaries, etc., etc., and by him reprinted at his own Private Press at Eastbourne. Then it attracted the notice of Sir Walter Scott, who praised it, not me, unconscious of the Author. Afterwards Macaulay (Lord) extolled it in his History of England. All these years the Song has been bought and sold, set to music and applauded, while I have lived on among these far away rocks unprofited, unpraised and unknown. This is an epitome of my whole life. Others have drawn profit from my brain while I have been coolly relinquished to obscurity and unrequital and neglect.

Don't we all know the feeling...