I'm glad somebody else has found this strong tune familiar,it's been nagging me for some time.To me it sounds like one of the tracks on my Jimmy Shand compilation CD.JS trotted out tunes by the handful,so it's difficult to tell which one you're hearing but I've narrowed it down to the Laird O'Thrums or Lady Anne Hope,believed trad.
I've looked these up on JC's excellent tunefinder,but they do not appear to match the Shand versions.
I heard M.Nyman interviewed on the radio and the Lloyds ad./Piano was mentioned,so he is credited for that.Now,there is a respectable history of composers incorporating traditional tunes e.g.Dvorak,but they acknowledge the source.If this one really is traditional,I wonder if M.Nyman has acknowledged it,or even realised? Or perhaps he's just changed the key to lay claim-the Shand was in G.
I understand about guests,but really,I'm just passing. Cheers-Blx