You are conflating skin colour and culture. A non-white immigrant who speaks fluent English, and is from a country with a common law legal system and British influenced culture can integrate far better than someone from a European country who does not speak good English. There are more people in London whose "main" language is Romanian, Spanish or Polish than any other languages.
Only 4% do not speak English well. London has had a large foreign born population and a lot of immigration for a long time and was fine in the 1990s so i doubt things have changed as much as you think in recent years.
By this logic, people should still be hanging out in the streets in all those villages where the master race dominates. And yet, we still only observe the bums and the retired hanging out with a day to fill. Any idea how that impacts your hypothesis?
