Let's be honest - they're not.
White - 5,209,900 - 69.4% (White British 58.0%; White Irish 2.5%; Other White 8.9%)
Mixed - 259,800 - 3.5%
South Asian - 982,600 - 13.1%
Black - 803,700 - 10.7%
East Asian or Other - 256,300 - 3.4%
Source.
To be fair, 30% of Londoners not being white is pretty shocking.