Most history textbooks cite the 1833 Abolition of Slavery Act as the end of slavery in the British Empire. Oftentimes it is heralded as evidence of Britain's liberal if not benign form of imperialism. However, the law was initially only applied in the West Indies. While 1833 act is certainly a landmark in the history of slavery, historians point out that it only signaled Britain's intention to gradually end slavery in the colonies.  In fact, Britain continued to profit from slave labour in the colonies for several more decades. Slavery was only abolished in the Gold Coast in 1874, in Gambia in 1906, and in Nigeria in 1916.

It is ironic that Sierra Leone, a colony founded for freed slaves, should be the last British colony to outlaw slavery. In 1901, Sierra Leone passed an ordinance ending the slave trade, but individuals could still bring slaves into the country for their own use. Despite this measure, in 1924 colonial officials reported that there were 219,275 slaves in Sierra Leone, 15% of the total population.  Even by 1924, British officials sheepishly admitted that slavery was still practiced in Sierra Leone, Nigeria, Gambia, Aden, Burma and Hong Kong.

Under increasing pressure from the League of Nations, the British colonial government finally declared the abolition of slavery in Sierra Leone on 22 September 1927, to take effect on the first of January 1928. 

Sources:

1. Wearing, D. Celebrating the bicentennial anniversary of slavery's abolition ...121 years too early. The Democrats Diary. website:.democratsdiary.co.uk
2. Hanlon, J. "Response The 1833 Abolition of Slavery Act didn't end the vile trade" The Guardian.  25 January 2007