Excerpts from Books and Wikipedia
"In 1771, Britain had effectively abolished slavery at home....William Wilberforce continually raised the issue in Parliament, until his success with the 1807 act--although it had some unforeseen ramifications, such as quadrupling the price of an able-bodied male slave in the United States in the early nineteenth century. As a result, some British captains were tempted to defy the law. If their ships were in danger of being searched, they threw the slave overboard. Hence, in 1827, slave trading was declared tantamount to piracy and so punishable by death. Then in 1833, slavery itself was made illegal throughout the British Empire." [1001 Days]