Rich,
I did say 1939, which would exclude the detritus from WW11.
As far as the one hundred thousand Africans rescued(?) from the slave trade, I'd like to see evidence of that statistic. I was thinking of immigrant intake and admittedly the rampaging Danes and their like came over a thousand years ago, but England's brush with foreigners was the Spaniard selling onions from their bicycles and Dutch fisherman plying their wares in Hull, Whitby and Scarborough.
I know one thing for a fact..... you could not vote in Spanish, French, Swahili or any of those other strange tongues, hence my feel for homogenity.
One last bit on Enoch Powell, ever considered the racist, he was the only person in Parliament who vociferously objected to the maltreatment of Mau Mau members by British security forces in Kenya, this, some decade before his other more inflammatory speech.
Re the slave trade, one of my paternal ancestors, Henry V. Huntley captained a ship in the Anti-Slavery campaign started by Wilberforce. I had no idea that so many slaves were brought to England, I thought most went to the West Indies.