Africans brought to Britain often tried to liberate themselves by running away and were pursued by their former masters. The courts were used as a means to both protect them from being forced back into slavery and to challenge the legality of slavery in Britain.
The first challenge came a long time before the organised campaign in 1690, when Katherine Auker challenged her master's right to his slave's labour in the Middlesex County Court. She called on the Court judge to grant her the right to leave her cruel employer (who had beaten her and thrown her out) to work for another. The court ruled she could find work in England with another employer but only until her original master returned to his Barbados estate.
The courts continued to be used to challenge the notion of slavery in England. The most famous case occured in 1772 when Granville Sharp, a committed abolitionist, defended James Somerset, an enslaved African, who had escaped and been recaptured. This proved to be a crucial test case in which Sharp argued that slavery was unlawful in Britain. The black community followed the case closely and maintained a presence at the court. The judge, Lord Chief Justice William Mansfield, eventually ruled that slaves could not be forcibly removed from Britain. The judgement was celebrated by over 200 Africans in a Westminster public house.
Although this ruling did not outlaw slavery in Britain, it provided a legal avenue for many enslaved people to obtain their freedom. However, the limitations of this protection were shown in 1783, when Sharp was prevented from bringing a prosecution for murder against the captain of the slave ship 'Zong'. This was despite clear evidence that 132 slaves had been thrown overboard. Judge Mansfield ruled that the dispute was an insurance claim, not murder.
The case highlighted the injustice and inhumanity of the Slave Trade and did a lot to convince many influential people that the law itself needed to be changed.