Thanks for the additional detail, Derek. All of that fits in with my own understanding of the situation, and I certainly remember Harry singing 'Begging' to the original Whitehead tune.

I've talked this over by email with Marcus, and he was kind enough to copy for me the note in MacColl's The Singing Island to Four loom Weaver:

"The version printed here was noted from the singing of Becket Whitehead of Delph, near Oldham, in 1947. Mr.Whitehead, at that time nearly eighty years old, had learned the song from his father, himself a hand loom weaver, and an active Chartist"

So MacColl was definitely claiming that BW sung it to him, not just supplied the words (and, according to Harland above, the song would indeed have been current in his father's day). However, in the light of the recent Scarborough Fair research, I'm still sceptical that the MacColl tune was ever sung to him by BW. And why, come to that, didn't BW sing it for Seamus Ennis and his tape recorder five years later?