[bloak]

> the association with an old British poem

Wait, are you sure about that? Wikipedia says "an 1869 minstrel song". I had assumed it was a song from the USA that happened to be fairly well known in Britain.

Also I have the impression that the word "nigger" is not traditional in British English. The first time I came across the word was when reading Mark Twain. I had previously heard several words used for referring to darker-skinned people but not that one. Of course that's just my experience from one part of the country.