In answer to Joop:
As there is no noted version of the tune now known as The Wild Mountain Thyme, neither printed nor referenced in any traditional or scholarly periodical, before the McPeakes sang it then we must assume the tune belongs to them. It has no similarity whatsoever with Tannahill’s chosen melody, The Three Carles o Buchanan or R A Smith’s first printed version of the tune we now “normally “use for The Braes o Balquhither.
McPeakes lyrics are obviously mostly taken from Tannahill and could be a rewrite from memory.