"The earliest form of 'protest' or political songs in England were put together in 'The Political Songs of England (From the reign of John to that of Edward II) by Thomas Wright (1839)'

They are in French, Provncál Latin, Anglo-Norman and early English and all come with a descriptive commentary and extensive notes - they date from the beginning of the 13th century."

Thanks, Jim, just what I was looking for when I saw the Winstanley reference. I knew there must be something like that.

Wright's songbook can be viewed and downloaded in various formats at archive.org:

Political Songs of England

Archive.org is a marvelous resource for public domain material of all kinds. Just two other examples: Both the Child ballad texts are available there; the Grateful Dead have made archive.org the organ for distributing ALL available unreleased and bootleg concert recordings.

I imagine they have a lot of pre-1924 songbooks, and I believe sheet music as well.