In December 1771, a man named James Somerset was confined in irons on board the Anne and Mary, a ship then anchored in the Thames. Somerset, who had been a slave in Virginia and Massachusetts, came to England with his master, Charles Stewart, in 1769. After absconding from Stewart' service, he was recaptured in November 1771 and, on refusing to return to his master's service, handed over for transportation to Jamaica, to be resold into slavery. Fortunately for Somerset, his plight caught the attention of anti-slavery leaders John Marlow, Thomas Walkin and Elizabeth Cade, who, with the help of Granville Sharp, petitioned the Chief Justice Lord Mansfield for a writ of habeas corpus to release him. The case that followed represented a landmark in the history of British attitudes to slavery, because when Lord Mansfield announced his verdict in June 1772 he found that, because enslavement could not exist without a positive law to uphold it, it could not be enforced in Britain. The precise implications of Mansfield' decision are contested; some historians see it as marking the abolition of slavery in the metropole, while others argue that its significance has been exaggerated, because de facto slavery continued after this date. Whether it materially altered the conditions of servitude for Africans and Asians in Britain, Mansfield's decision did formalise emerging assumptions that slavery was incompatible with British subjecthood. ‘The spirit of liberty is so deeply implanted in our Constitution, and rooted even in our very soil,’ William Blackstone noted in his Commentaries on the Laws of England (1775), ‘that a slave or a Negro, the moment he lands in England, falls under the protection of the laws and so far becomes a freeman, though the master's right to his service may possibly still continue.’

Just as Mansfield was forming his judgment, 8,000 miles away in Calcutta the Committee of Circuit in Bengal was considering plans for the more effective regulation of justice in the EIC's newly acquired Indian territories. In the same month that Mansfield delivered his decision, it put forward a novel and controversial plan for dealing with the dacoits (bandits) who had been plaguing the region.