Ballad opera tunes. I'm sure this was common practice though it's highly unlikely this was exclusively the case.

The tune used today on the folk scene was probably added when the later version from the 19th century was rewritten. The oral version in Purslow's 'The Constant Lovers' under the title 'Well Met, Pretty Maid' is recognisably related to Arne's tune, however plagiarised.

As for the texts, it's a well-known fact all of those ballads about Napoleon and the Napoleonic Wars go back to Roman times or earlier!

Of course things of value can be and are created by the PEOPLE. There are plenty of examples, but if they created all of the broadside ballads exactly how did they become so widespread? If you mean the broadside hacks living in the towns and cities near the printers were part of the PEOPLE then we are in accord.