Very tempting to say, London was a port city at the centre of international trade and a global empire: it was ethnically diverse. Get over it.
It’s not as though this is some new millennial ‘politically-correct’ whim. Peter Fryer’s classic work Staying Power: The History of Black People in Britain was published in 1984 and is still considered the definitive study of the Black presence in Britain since Roman times. More specifically on the Georgian era, Gretchen Holbrook Gerzina’s Black London: Life Before Emancipation came out in 1995 and shows that there were identifiable Black individuals with agency in their own lives, living in London at this period. More recently, David Olosuga’s Black and British: A Forgotten History (2016) covered similar territory. See also the Digital Exhibitions at the Black Cultural Archives and the helpful Community History: Black Communities at the Proceedings of the Old Bailey online site.
There was also, particularly around the docks, a more or less transient population of lascars: East Indian seamen.
The slave trade had been abolished in 1807 and slavery was illegal on English soil. However it was still legal in most other parts of the British Empire, in other European countries, and in the Americas. It was hoped that abolishing the trade in African slaves would cause the institution itself to wither. This was an over-optimistic idealistic belief. A thriving illicit maritime trade in slaves continued, against which the Royal Navy sent patrols. Slavery in the British Empire was not abolished until 1833 and only then at the immense cost of massive compensation to slave-owners.
L.A. Hall, FRHistS