I think it's natural for first (and to an extent, second) generation immigrants to socialise mainly amongst themselves. It is the same with British ex-pats... in fact, the Brits are possibly the best example of this. It's a shame, but it's also understandable. It is not done from any desire to avoid the native population, it is simply because it's easier to make friends with someone who shares your language, culture, customs, cuisine, religion, etc. I don't view it as a big problem, and furthermore, I think things are changing. The world is becoming more integrated... we're becoming more aware of each other's cultures and taking more of an interest in them. People in the UK - and I would guess London in particular - are more familiar with other cultures than ever before, and people have started to view the cultural mix as a benefit. Mixed race relationships are becoming much more common. There is more equality in education and in the workplace, helping people broaden their social circles. Second generation immigrants are feeling increasingly "british", while still keeping in touch with their heritage.