Fred Wedlock came to fame on the UK folk circuit at about the same time as many other "folk-comedians". It seemed to be a regional sort of thing, that is every region had it's own comedian. Fred was the West-Country version, just as Jasper Carrott came from the Midlands and Mike Harding from the North-West.
I believe the Boxer parody is entitled The Folker and the double-entendre would have been intentional.
I think the penultimate verse should read:
"And in Sir Patrick Spence, I clean forgot the 42nd verse,
So I sang the 27th --TWICE AS LOUD--and in reverse, and no one noticed..."
AndyG