Paul Burke, we're not necessarily talking about the British (or English) army. There were quite a few English or Scottish mercenaries around in Europe's armies, in the Thirty Years' War and also, I believe, in the Napoleonic Wars.

Trevek, Hamish Imlach claimed years ago (obviously ...) that the School of Scottish Studies was working on a study of precisely the scope you are looking for. I never heard anything about it again, but it might be worthwhile asking them. This should take you to their website.