And within less than a century, Britain was leading the international effort to end slavery in Africa, and they did it.
Uncle Tom's Cabin was a bestseller in Britain. Some historians credit it for helping to prevent Britain from aiding the Confederacy during the Civil War.
Some of Britain's elite wanted to lend military support to the CSA. British industrialists still got much of their cotton from the South. But so many common British voters were rooting for the North, Parliament declined aid to the CSA. They decided to focus more on India for their cotton needs.
So on balance, Britain did far more to end slavery than to preserve it. More than any other modern nation.
England enabled slavery to continue for years, because they controlled the high seas trading, and most slaves came to the US via British ships, before Wilberforce was able to end their participation in the slave trade. Slavery was outlawed in England, but not slave trading. Without English ships slavery would have most likely died away a lot earlier due to lack of slaves.