As a British taxpayer - yeah, I was aware of this.
I've even seen it twisted into "This is how moral we were - in our attempt to end slavery, because of how immoral it was - we even paid slave-owners to stop slaving! It was the only option, and a difficult decision, but it was worth it to stop slavery! Yay us!"
Like - *mate*, we once had the military might to have "owned" about 1/4 of the entire population of the Earth, and instead of saying "lolwut fuk you slaver, you see all these guns? Free the slaves or else, you bell-ends", we paid them off instead?
side-note - I've lost the link now, because it was bookmarked on twitter, but I've seen credible evidence to say that the Brits were "instrumental" in ending slavery *only when* it was in our best interests to do so.
Essentially (the details may be wrong, I'm going on memory, it's been a while), we'd recently subjugated India and had a ready supply of "not-slaves", and were in danger of being out-performed by the French who were angling at a slave colony (apologies, I don't recall exactly where), so it was in our economic interests to drum up support for outlawing slavery in its strictest sense, in order to out-perform the French.