New research into British involvement in the slave trade shows that enslaved African people were branded with an identifying mark bearing the British Crown emblem.

Prof William Pettigrew, who led the Register of British Slave Traders research, described the imprinting as a “dramatic and harrowing” symbol of the monarchy’s relationship to slavery.

The research offers the most comprehensive examination of a national community of slave traders ever attempted.

Since 2021, Professor William Pettigrew has led a team of nine historians in a project to unearth every known investor in Britain’s transatlantic slave trade. The Register of British Slave-traders launched today, presents biographical data related to each of the known investors in the transatlantic trafficking of enslaved African people from the sixteenth to the nineteenth centuries. Drawing on what is now known of these 13,000 individuals, Professor Pettigrew has written a new version of Britain’s history which tells us who these traffickers were and reveals – for the first time – the impact they had on the nation’s development during this formative era.

Dr Nicholas Radburn, historian at Lancaster University and co-investigator in the project, told the BBC he first found the identifying mark – which is an image of the Crown, with the South Sea Company logo below it – while looking through the company’s archives at the British Library in 2022.

Founded in 1711, the South Sea Company was set up as a public and private British company and trafficked thousands of enslaved Africans.

Radburn said it was “remarkable” to find records of the branding – first reported by The Guardian, – “buried in a very nondescript sounding volume: ‘The Register of Instruments'”.

In 2024, he found letters that helped piece the story together. They were from the company’s director to their “factors” (slave traders) in the Spanish Americas, Radburn explained.

“The letters were full of very detailed instructions on how to conduct the slave trade,” he recalled.

One letter from February 1714 was “exceptional because it laid bare so clearly the ways in which the London-based directors were personally involved in the violence that was committed against the enslaved in the Americas”.

The directors supplied English-made irons for slave traders to brand enslaved African people on the left shoulder with the emblem. The letter said the mark was intended to distinguish the company’s enslaved people from others.

The researchers say the register reveals how widely financial support for the slave trade extended, from monarchs and politicians to plumbers and clergymen.

“They financed wars, shaped modern industry, and built ports, canals and thriving cities, helping make Britain a global and imperial force,” Pettigrew said.

Anyone who contributed financially to the transatlantic slave trade, or to a company enabling the trade, is listed in the database. “They were a tiny minority but their wealth, power and appetite for risk influenced not just Britain’s economy but its politics, science, arts and institutions – from the development of the Royal Navy and the restoration of the Stuart monarchy to the emergence of two-party politics, the free press and Parliament itself. They financed wars, shaped modern industry, and built ports, canals and thriving cities, helping make Britain a global and imperial force,” Pettigrew concludes.