I m talking about the fact of what is happening.
You certainly are aware of the fact that the people with African ancestry arrived on the British Isles in Roman Britain. ( Severus, an African, was Roman emperor from 193 to 211.)
During the Anglo-Saxon period and Medieval age, Africans were likely either slaves or bonded servants.
Later, "blackamoor servants" were perceived as a fashionable.
Similar a bit later in any nation which had colonies in Africa or where Africans had settled historically since centuries (like on the Iberian peninsula, Italy, etc)
There certainly is a "mechanism". Don't they teach history where you live?