I don't suppose there's a prize for the 'catter who resurrects the oldest thread, but I'm surprised nobody said that this song is virtually identical to Six Dukes Went A-Fishing or The Royal Duke of Grantham, and there is a suggestion there of a possible historical tie-in:

Strongest suggestion on the background is that the incident refers to William de la Pole, first Duke of Suffolk who was murdered by political enemies & his body tossed on the sea-shore at Dover in 1450. This was mentioned in Shakepeare's Henry VI, Part II, Act 4. A broadside on the song appeared in 1690. AJS Are you still with us Ian?