"Define "traditional British culture""

Visit 'Britain' - then visit 'France' and you'll get an idea of the panacea of cultures and sub-cultures within those two nations, that are quite distinct from one another, most of which could be very readily labeled as either 'French' or 'English'.

And that would only be two of many nations.

Yes - culture and ethnicity actually exist in the world.

That's what actually makes it 'diverse'.