The abolitionists used many ways to convince people that the slave trade should be abolished.
As the ideas of the Society for the Abolition of the Slave Trade grew in popularity, a network of local abolition groups was established across Britain. These groups campaigned through public meetings and the publication of pamphlets and petitions.
Before the days of radio, television and the internet, public meetings were the best way to gain publicity for a cause. One of the main speakers at abolitionist meetings was John Newton, a former slave ship captain who became an abolitionist.
The Society for the Abolition of the Slave Trade tasked Thomas Clarkson with gathering evidence of the evils of the slave trade.
In 1786, Thomas Clarkson’s 'An Essay on the Slavery and Commerce of the Human Species' was published. Clarkson’s role was to collect as much damning evidence about the slave trade as possible.
He visited slave trading ports such as London, Bristol and Liverpool, where he boarded and investigated slave ships. He collected evidence such as iron handcuffs, branding irons and thumbscrews.
In 1787 Thomas Clarkson went on a five month speaking tour of Britain, showing people chains and irons and a model of a slave ship. This was to stir up opposition to slavery.
He also spoke to over 20,000 seamen and found out that they too suffered from the slave trade, as their captains didn't care if they lived or died. Clarkson’s investigations angered some ships' captains and they tried to kill him by pushing him into the dock in Liverpool. They failed and Clarkson survived.
One of the most important pieces of evidence Clarkson gathered was a diagram of the Liverpool slave ship, the Brookes, showing the cramped conditions in which 450 slaves were stowed below decks.
Other campaigners also published leaflets describing conditions on the Middle Passage and atrocities such as the Zong incident 1781.
During the 1770s the abolitionist campaigner Granville Sharp campaigned against the slave trade through the law courts.
Granville Sharp won the Somersett legal case 1772 in London. Chief Justice Lord Mansfield (himself a slave owner) ruled that slaves in Britain could not be forced to return to the West Indies.