Researcher Malik Al Nasir bought historical documents while investigating his family history – and began building an archive

A bundle of letters discovered for sale on eBay by a man researching his roots has cast new light on the lives of prominent British families who amassed a fortune from slavery.

Documents detailing the affairs of 19th-century families linked to Sandbach, Tinne and Company, a business that dealt in enslaved people, cotton, sugar and coffee, were being traded online by collectors of rare stamps and postmarks.

But the letters’ significance to the study of colonialism was appreciated only when Malik Al Nasir bought a tranche of them while researching his own family history and began building an archive.

The letters now form part of the University of Cambridge’s landmark Sandbach Tinne collection, joining Isaac Newton and Charles Darwin’s papers in the university’s prestigious Cambridge Digital Library.