The 1833 Abolition of Slavery Act is usually cited as the end of slavery in the British empire. But, as Gott notes, it was always intended to only "gradually" end slavery, and the law was initially only applied in the West Indies. Slavery was abolished in the Gold Coast in 1874 and in southern Nigeria in 1916. In 1906 in the Gambia, an ordinance was approved that anyone born after that date could not be enslaved, but remaining slaves were to be freed only on the death of their masters.
In 1901, Sierra Leone passed an ordinance which ended the dealing in slaves, but individuals could still bring slaves into the country for their own use. The same ordinance did allow slaves to buy their freedom, at a sum to be fixed by the governor of not more than four pounds for an adult and two pounds for a child. When the governor wanted to abolish slavery there in 1921, Winston Churchill, then secretary of state for the colonies, replied that "the abolition of slavery could not, however, have any immediate beneficial effect on the finances of the colony" of Sierra Leone.
By the early 1920s Britain was under increasing pressure from the League of Nations temporary slavery commission. In 1924 Britain was forced to admit that slavery was still practised in Sierra Leone, northern Nigeria, Gambia, Aden, Burma and Hong Kong.
Sierra Leone was founded for freed slaves (some in the American revolution had been promised land and freedom if they fought for Britain, but the land turned out to be in Africa). Captain WB Stanley, commissioner of the Northern Province, reported in 1924 that there were 219,275 slaves in Sierra Leone, 15% of the total population. Governor Sir Ransford Slater wrote that year: "My first impression [on arrival] was one of surprise that in Sierra Leone, of all colonies, having regard to the history of its first settlers, there should still exist, even in the hinterland, an admitted form of slavery."
Britain in 1926 signed the League of Nations slavery convention. But it was quickly in trouble with the League, following a ruling by Sierra Leone's supreme court on July 1 1927, which declared that the status of slavery "is clearly recognised" and thus "the use of reasonable force [by the slave's owner] in retaking of a runaway slave must also be recognised". Court president Mr Justice Sawrey-Cookson added: "It must be as absurd to deny an owner of a slave his rights to retake a runaway slave as to deny a husband certain rights which follow on a lawfully contracted marriage."
Slavery was finally abolished in Sierra Leone on January 1 1928, nearly a century after the Abolition of Slavery Act. In marking the end of slavery, this is the date which should be used.