Dr Gardiner noted only the words from Mr Wigg; the tune was taken down by one of his collaborators. At the moment I don't know which. Probably J F Guyer or Charles Gamblin; but that's one of the wee details that I'm hoping to check in the near future.

Vaughan Williams had nothing to do with it, though as Mick points out he did "collect" another example elsewhere, and indeed used that tune (as Forest Green) for O Little Town of Berthleham when he revised the English Hymnal. There's another set from tradition (Scottish this time) in vol III of the Greig-Duncan Collection.

The song was issued on broadsides, of course. Two editions of the early C19 can be seen at Bodleian Library Broadside Ballads:

The plough-boy's dream

An earlier edition of the late C18 can also be seen; the Bodleian indicates that it was written by William Mason.

The plow-boy's dream