Is Variety not Just the Spice but the Growth Factor?

The UK census has been released and shows some fascinating glimpses of the changes in the UK. For example that in London, white Anglo Saxons account for less than half the population, and that immigration is heavily focused on the South East. But I ask isn't this also the area of Britain growing the most and showing the most resilience financially? Is it that the immigrants went there because of the growth or that the immigrants led the growth? That makes me look at where else huge mixed populations exist and once immediately thinks of Singapore, Hong Kong, New York, Sydney, Los Angeles, Sao Paulo all hugely successful vibrant cultures and all in massive sustained growth. Does this actually tell us that stable less miscegenated populations are less likely to grow and succeed? People complain about immigrants and jobs and housing, but the fact seem to indicate that the North of Britain is actually a population of original British with little immigration, and yet this is where there are no jobs and house prices are the lowest in the country. Worse its the area with the least new businesses and opportunity.