London and the South-East are incredibly mixed. I believe that recent statistics showed that 50% of Londerers were not born in the UK or was that in London. I can't quite remember. Anyway it is perfectly normal for school kids from the South to have very mixed classes with people coming from lots of different countries, ethnic groups, mixed race families etc etc. Half my class were mixed something - Dutch/English, Irish/German, Italian/Scottish or of various different family backgrounds - Chinese, Nigerian, Korean, Seikh, Iraqi, Trinidadian, Scottish, Welsh, Jamaican grandparents, Lebanese and quite a number of asians, some whose families came from India, some from Pakistan and from various countries in Africa....the list goes on. And this is pretty typical for London.
Coming from London, I find it extraordinary that the North-East appears to be so different. Come to think of it I never met anyone from the North-east before I was 17.