The status of slaves as property was long established. The use of the property law meant that the enslaved were not considered humans, but commodities.
In 1729 the joint British Attorney General, Sir Philip Yorke and the Solicitor General Charles Talbot were asked to consider whether a slave could be freed. They expressed the opinion that a slave was the master’s property and could not become free.
We are of the opinion, that a slave, by coming from the West Indies, either with or without his master, to Great Britain or Ireland, doth not become free; and that his master’s property or right in him is not thereby determined or varied.Sir Philip Yorke, Charles Talbot
The Somerset Ruling of 1772 concerned a slave’s liberty and status as property. The slave in question was James Somerset, who had escaped from his master while in England. He was recaptured and was to be transported to Jamaica. The case centred on whether slavery, which was tolerated in the colonies, was compatible with English law. The final decision of Lord Chief Justice, Lord Mansfield, was that no slave could be forcibly removed from the country and resold.
No master ever was allowed here to take a slave by force to be sold abroad because he deserted from his service.Lord Mansfield
But this was not the same as saying that slaves in Britain were now free. The legal position of African slaves remained unclear until the early 19th century.