Here:
"WAV, at what point does something become English?"..don't know - ask Sedayne when he decides I am once again English, and How long is a piece of string?"

So why, then, can't ceilidh be considered an English term, if it has been widely used as such for several years?

Anyway, how do you reconcile the above quote of yours, with this one:
"Critics often mention cut-off points for English culture, and evolution/change, when it's mainly a case of REPLACEMENT: i.e, if an English person is singing an American song in an American accent they are not performing an aspect of their own English culture/if a Swedish tune is being played at a session of English folkies, one of our many fine English tunes is not being heard."