G'day Kiwi,I know the song as I heard it from Ewan MacColl and he definitely sang a Scots version. This certainly doesn't mean that it was originally Scots. I seem to remember that A.L. Lloyd reasoned that many songs that were English, or had currency across the UK, had been forgotten in England because that was the centre of change, the hub of the Empire and all that guff.
He felt it legitimate to take such songs and sing them as English - even substituting English tunes - and there is some validity to this approach to rebuilding a partly lost tradition. An unfortunate side effect, to which I referred in the original posting, is that the words that survive in (say) Scotland have settled into a Scots rhyme scheme.
Actually, if you look at old English spellings and vocabulary you find that the further back you go, the more it looks like Broad Scots. The language also has changed faster in the London/Oxford/Cambridge triangle than in more traditional areas and it is quite possible that the song is an Old English song best remembered in Scotland. Remember that Child had more luck collecting old English song in the Appalachians than he did back home.
Regards,
Bob Bolton