IMHO most British people did not see a black face until the 1940/50s and the coming of post war immigration.
I can imagine some truth in this.
As mentioned in a previous thread a while ago, my Granmother grew up in Italy during WW2 in a region north of Naples and south of Rome, in the same area of Monte Casino.
Apart from having to host ungrateful German soldiers, she also witnessed the Americans moving through the area as the conflict wore on.
One thing she clearly remembers is being scared of the black American soldiers as no one had ever seen black people before.
She says they were referred to as black devils, although she never said they did anything particularly devilish or acted badly, it must have been an eye opener for her as a child.
I don't imagine there was much interest for people from Africa to move into equally as poor areas in Europe back then, unlike nowadays.
Not saying it never happened, but I imagine it was extremely rare.