John's great-grandfather was kidnapped in Africa and sold as a slave in Kingston due to the sugar trade. (TV: Remembrance of the Daleks [+]Ben Aaronovitch, Doctor Who season 25 (BBC1, 1988).)
Behind the scenes[]
Although the location of Kingston is not mentioned in Remembrance of the Daleks, from John's accent, it is obviously the city in Jamaica. In real life, Kingston is the capital of Jamaica.