One only needs to look at the Glorious Revolution to see what a hostile takeover of Britain by a foreign power which pays lip service to Britishness would look like.
Also one rather needs ones army to be xenophobic, a xenophilic army would be somewhat poor at its job.
I've been musing that the majority of ~canon fodder~ lower class working men are so destructively disengaged from main stream western culture that a new branch of Islam with 19th century western sensibilities - nationalism, nativism, chauvinism, etc. - would have very little trouble in taking over.