Demographic studies of London show that less than half of Londoners are ethnic British white. Does this indicate a welcoming multi-ethnic and multi-cultural society, or a dangerous dilution of "Britishness"? Is London REALLY another country?

Given that the City of London is virtually another city, I guess that's possible.

I can't speak about England but the influx of migrants -- particularly from Asia -- has had two effects. It has widened our perspectives and our acceptance of other people (Oz was very racist when I was growing up) but it has also polarized the haters. Such people become more vocal and are given to displaying bumper stickers liked "Australia: Love it or Leave it." In that, they're very much like the American gun lobby who love to quote the NRA's slogans as though they are  holy script.

As for weakening the Anglo-Saxon bloodlines, I think that is probably inevitable. The lines between IC1, IC3 and IC5 are likely to become blurred so that crime shows are likely to put out an APB on an "IC3.75 male". I don't think that's a bad thing.