Here's what my source says:

First appeared in print in 1840's as new words to the old air "Kind Robin lo'es me." Taken down by Sir John and Lady Scott from "a poor little boy who was singing on the streets of Edinburgh" in the 1820s. May date to the 1740s, referring to the hurried retreat of Bonnie Price Charlie from his English campaign.

If this chronology is correct, it would turn to pure supposition much of the interpretation I've read about the "high road" and "low road," etc.

Jeff Walker