"spoke" rather than "broke" surely?

BTW Scott didn't have the now-familiar tune in mind - he was pastiching older songs to the tune "Bonny Dundee" (as found in the Skene MS of the early 17th century). "The Lords of Convention" tune dates from the 1840s; it's from a piano salon piece, "The band in the distance". Scott himself was almost tone-deaf and may not have noticed the difference between them.