There are several threads where this is discussed Ed, but the basic idea you can get from this post by Sandy:

Subject: RE: Help: real origin of Wild Mountain Thyme
From: Sandy Paton
Date: 05-Apr-00 - 02:01 PM

I recorded it for Elektra Records in 1959 (and taught it to Judy Collins in that year when she and I worked together at the Exodus in Denver). I had learned it from a field recording made of the McPeakes which I found in the BBC Recorded Programmes Library which was then housed at the Cecil Sharp House in London. Elektra was never sued by the McPeakes, which makes me wonder about the date of their copyright filing. Perhaps it was simply the obscurity of my Elektra album that served to protect Elektra. It did not, to put it mildly, overwhelm the early folk revival world. (wry smile emoticon inserted here)

In earlier threads on this subject, I think I have pointed to several other traditional versions of the song, including those collected from Carrie Grover in Maine. There is plenty of evidence to show that Francis McPeake's song is an adaptation of an older Scottish song derived from a Tannahill poem. I'll let the chips off of the old copyright block fall where they may.

Sandy

**********************************************************************

Spaw