StingingVelvet: Hahaha... I really don't. Nor do I think a country with a 3% Black population like the UK is "conservatively represented" by having every single companion in the RTD era be in an interracial relationship.
SheBear was kind enough to compile a list for you so we don't have to cover why you are wrong on the every relationship point. Furthermore, to quote Wikipedia:
20.9 per cent of Londoners are of Asian and mixed-Asian descent. 19.7 per cent of Londoners are of full Asian descent, with those of mixed-Asian heritage comprising 1.2 of the population. Indians account for 6.6 per cent of the population, followed by Pakistanis and Bangladeshis at 2.7 per cent each. Chinese peoples account for 1.5 per cent of the population, with Arabs comprising 1.3 per cent. A further 4.9 per cent of Londoners are classified as "Other Asian".
15.6 per cent of London's population are of Black and mixed-Black descent. 13.3 per cent of Londoners are of full Black descent, with those of mixed-Black heritage comprising 2.3 per cent of the population. Black Africans account for 7.0 per cent of London's population, with 4.2 per cent as Black Caribbean and 2.1 per cent as "Other Black".
5.0 per cent of Londoners are of mixed race.
In January 2005, a survey of London's ethnic and religious diversity claimed that there were more than 300 languages spoken and 50 non-indigenous communities with a population of more than 10,000 in London.
And do keep in mind that the TARDIS travels in both time and space. So that mysterious 3% you desperately cling to is moot, regardless.