[dghf]

> it begs the question as to where the population went to

I'm guessing they married out.

I cannot find a reference, but I seem to remember learning that eighteenth century Covent Garden in London had a significant black population, possibly former slaves freed by and then recruited into the British Army during the Revolutionary War. Within a century, that population had gone, at least as a distinct, visible group: the original population were all male and had taken local wives.

[pjc50]

Google delivers: "roughly 10,000 [black people] in London" in the late C18th.

https://books.google.co.uk/books?id=CCd8AwAAQBAJ&pg=PA8&lpg=...

[yandago]

>I cannot find a reference

Stop here.

[dghf]

Why? Someone might know what I'm talking about and provide the reference that eluded me; or, just as usefully, they might be able to demonstrate I'm speaking nonsense.