But surely, logically, only a shellfish salesperson, steeped in the practise of fishmongery, would have known that cockles and mussels were sold "alive, alive-o" from wheelbarrows? Equally surely, a busty young maid, and not one for covering up her ample busoms, would have been susceptible to a "fever"? So it MUST have its origins in the oral tradition predating the bad-poet hacks of Edinburgh and was, logically, written by a working-class hero?

Too much insider knowledge to be fictitious ;0)