I don't think anyone is suggesting that there hasn't been a lot of racism in the British Isles, or there still isn't a great deal. But there have been, and continue to be, some significant differences between racism here and across in America.

With the end of slavery the relatively small black population which had been built up was absorbed into the general population. From then on until the 1950s, outside of sailortowns, black people weren't visibly present - they were probably generally thought of as another lot of odd foreigners, and like all foreigners, rather funny, and not really to be taken too seriously. "Johnny Foreigner" was a term in use quite widely. (It still is in fact, though with a greater sense of irony these days.)

Out in The Empire, of course, there were lots of black people, but that didn't directly impinge on life back here. The official line, of course, was that The Empire was a good thing, and that being ruled by Britain was a good thing for the natives, who weren't really up to that kind of thing themselves.

American type blackface minstrel shows were popular enough during the 19th century, but the context in which they were existing was different from back in the States, since there wasn't any element of mocking a differentiated local black community. I am sure it woudl have been seen as just people dressing-up and painting-up weirdly and singing funny American songs.

There was a craze for banjos towards the end of the 19th century, coming largely out of this, and I suspect that when people were dressing up for street performances and so forth, experience of having seen blackface minstrels would sometimes have affected how they disguised themselves, in the same way that memories of Pantomime Danmes would have affected the way dancers in drag carried on.

With the arrival of sizeable black and Asian immigrant populations in the 1950s there was, for the first time in a long time, a range of non-white communities here, with their own traditions. That has had a great influence on popular music in England, including folkies. But so far as native folk music is concerned it's been more through a process of osmosis than anything, and I think it'd be hard to distinguish the influence from immigrant communities from the influence from America via the mass media. Except maybe for street processions sometimes, where Notting Hill has shown how it can be done.