The typical British black person could probably only name two or three prominent American blacks, namely MLK and whoever the world champion of boxing was at that time. Culturally, American blacks and British blacks shared almost nothing in common.
The influx of the typical American black behavior I would say started around the mid to late 80's, where Jesse Jackson, Sharpton, and all of the race hustlers at that time figured out to export their poison overseas.
And they gave the world the greatness of Ska.