How many people could centre their feeling of @brisishness' on colour and the majority religion? I don't think it's what makes you know what your country is. I would say that the weather, queuing, a ramshackle-make-do-Fred-Carno approach to things, bonfire night, windbreakds, humour etc are far closer to anything that you might call identity. This has been enriched by language (from everywhere!), food, old and enthusiastically newly introduced etc etc.
And that's before we get to 'acceptance' between English and Welsh, Scottish or Irish!!
'Britishness' has always been and still is on the move. Look how enthusiastically we have supplanted so many little things with American imports - you are an 'old fogey', probably, if you crave the original, and contrast that with the attitude to things we assimilate from ex-commonwealth countries, for e.g.
Thgis whole issue, for me, is unpleasantly underpinned by a sense that if there is a problem, it's now 'the immigrants' who need to change.
In the experience of my extended family, the actual immigrants 9i.e first generation, new arrivals) from ex-british colonies etc arrived full of a sense of 'britishness' which they were proud to hold and eager to apply. It is their children and grandchildren who have learned that however britsh their parents were, and strove to be, they would still subject to abuse on the street and ridicule in the press and light entertainment.
Where is the British stiff upper-lip? That was obliterated under a mountain of flowers in cellophane afyer Diana's death. And as for radical movements - they have always been bubbling under, from Welsh Nationalist arsonists, to the IRA to anilmal rights body-exhumers. All prpocluded in the laws which uphold our 'british values', just as the actions of newer radical groups are.