Since this thread was last current, I've found some additional information while looking for a tune for the DT file   JOCK SHEEP.  At the time we were discussing the MacColl recording of The Broomfield Hill as detailed above, I had looked briefly at a library copy of the Greig-Duncan Folk Song Collection (vol.2, 1983), but hadn't found the text or tune quoted by Bronson, which seemed odd; now that I have my own copy and can consult it at leisure, I find that the Aberdeenshire songs I referred to are not Broomfield Hill variants at all, but versions of Jock Sheep!  It appears that they were initially mis-classified and printed in Last Leaves as Child #43, presumably because of the similarity of the first verse, which I believe is all that appeared in Last Leaves; from where Bronson reproduced it in good faith.

It follows that neither of the first two tunes I quoted belongs to The Broomfield Hill at all, which makes MacColl's use of a form of it, "from family tradition", even more puzzling; as does his use of the Jock Sheep chorus grafted onto a Broomfield Hill text.  Of course, the tune from the J.K. Sharpe MS, apparently a relative and apparently having belonged to a Broomfield text (unrecorded) may have some bearing on the puzzle, but there's still that chorus...

It's hard in the circumstances to be entirely confident in MacColl's information.