David Linsley wants Nelson Mandela to make money for him. His purchase of a 24-carat black stone named after the former South African president and Nobel laureate was the first for a specialised diamond fund his investment company will start next year.

The “Madiba diamond”, named after Mr Mandela’s title as a clan elder, is a rare and hard stone. Mr Linsley fails to reveal how much he paid for it, but says it will be part of the fund his company, Sirius Investment Management, will start next year, comprising top-end stones each worth more than $1m.