the bells in various English cities ringing in relief when a bill to abolish the slave trade was defeated--after the 1770's.

Only the rich can get church bells ringing. Of course a large fraction of the British elite profited from the slave trade. Most of the streets in the centre of Glasgow are named after people who made their money that way (in case you hadn't noticed, Georgian street names were not decided by democratic vote).

That doesn't say a damn thing about the social attitudes of the vast majority of the British people, who had no stake whatever in the slave trade and often saw their own class interests as aligned with those of the slaves (see Marcus Rediker's recent book - Rediker is a rather more trustworthy source than a Tory plonker like Thomas, whose uninspiring book I have upstairs somewhere; I gave up on it fairly early on as it was telling me nothing I didn't already know, and for the period I was interested in, was telling me nothing at all).

Certainly by the 1940s, the whole idea of treating Black people as second-class citizens was something you would only EVER hear in the UK (outside elite circles) from visiting South Africans, Australians and Americans, of whom only the Americans had any influence. Even Mosley's Fascists didn't make an issue of it.

Look at "The Petition of the Sharks of Africa" on my website. That anti-slavery polemic from 1792 inspired a humungous riot (on the King's Birthday) in which the Edinburgh mob attempted to burn down the house of the man seen as central to the continuance of the slave trade. They very nearly succeeded. With better weapons they would have overthrown the administration of Scotland over the issue.

I take it you still haven't remembered any delta blues songs about WW2.