It just goes to further prove that everything "British" is in fact an import along with the migrants who have inhabited these shores since before the last ice age!

True but I think that it goes deeper than that.
We are a country of immigrants. Very few of us would b able to trace our roots back to being 100% English/Scotish/Welsh/Irish or probably even 100% British. I know I can't as I have Anglo-indian ancestry on my father's side.
But I was listening to a discussion on the issue of community and it was stated that a well known scientific element to the success of a community was that it should not change quickly. We are in an age where everything is quick (movement of data, food, transport, etc)
So maybe this reaction to a change in Britishness (which we know has changed over the decades and centuries) is actually a revulsion to a change which we feel is progressing too fast. We all hold community important, otherwise you would not be reading this post.
Personally I think that being British is what you make it and not what others feel it should be. Many Americans think we still wear bowler hats, quite a few french think we are all mono-linguistic food-heathans and we all know what the Chinese think!
I would say do not worry, stick to your beliefs, don't impose them on others, and roll with it. This is still a Great place to be
