I get the impression that most of these contributions to the folk canon started off in London as one might expect, the song cellars, glee clubs, Music Halls, pleasure gardens. Of course it wouldn't take long for them to be imitated in other large urban centres. Also London was the centre for printing with many more printers per sq mile than anywhere else in Britain and it follows that that's where most of the ballad writers were.

One genre that definitely started elsewhere was the minstrel troupe genre which came from America but soon hopped over to London c1840.

Yes, I believe the glee clubs were originally a middle-class thing, as you needed to be able to sight read. Books of glees, catches and rounds were very popular. Many of the glees were published singly in sheet music form, e.g., 'Dame Durden'. The earliest version of 'The Derby Ram' I have seen is on a glee sheet. I couldn't state that's where it originated, but it's possible.