Years after the fact, I've quite incidentally caught Malcolm (R.I.P.) out in a rare error -- which was corrected in his own newsletter, of the South Riding Folk Network (pdf online here):

It seems that we repeated something of an "urban myth" on the subject of Margaret's Waltz in our last edition. Janet Dashwood kindly wrote to set the record straight: "...the tune and dance were written for Margaret Grant on her retirement as EFDSS Representative in Devon, 1959. ... Margaret Grant did much work in Devon and the south-west teaching and encouraging dance, song and music."

~ Becky in Tucson