After sustained campaigning in Britain, the Slavery Abolition Act came into force in 1834 and finally banned slavery throughout the Empire. In order to free some 800,000 slaves, Parliament paid a huge £20m – a third of the Treasury’s annual income at the time – in compensation to the slave owners in the Caribbean, South Africa and Canada. And in 1843 Britons were forbidden to own slaves anywhere in the world.

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So many nations reneged on their promises that Britain placed a naval squadron off the coasts of West Africa, looking to intercept slave ships: the West Africa Squadron. This patrol, sometimes just a handful of ships, sometimes as many as 20, patrolled the Atlantic from 1808 to 1870, landing their human cargo at Freetown in Sierra Leone, a colony set up for freed slaves. Over 62 years the Royal Navy captured hundreds of slave ships and freed some 160,000 captives. Several hundreds of thousands more were saved by diplomatic and naval pressure.

This patrol was expensive both in money – a great deal of British tax payers money – and in life. Over 60 years or so patrolling the Atlantic, some 17,000 sailors died; some killed in action, some from the same diseases as the slaves they freed, including fever, dysentry, yellow fever and malaria. This represented one sailor’s life lost for every nine slaves freed.

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In Africa Britain made some 45 treaties with African rulers to stop slaving at source, however in some cases they had to be paid off. Quite often Britain was also invited to offer protection, for example Africans on the coast were being terrorised by the aggressive slave kingdom of Ashanti and requested British protection.

In 1839 the British Foreign Secretary Palmerston ordered the seizure of Portuguese slave ships and in 1845 his successor Lord Aberdeen declared Brazilian slavers as pirates and open to seizure.

In 1850 the British navy entered Brazilian ports to destroy or seize the slave ships, a decisive action in ‘persuading’ Brazil, the biggest slave buyer of them all, to end slavery.