The ex-chief of a Nelson Mandela charity is resigning from its board after the revelation that he secretly kept diamonds passed on to him by supermodel Naomi Campbell.

Jeremy Ractliffe said he kept the stones in a safe for 13 years until he handed them over to South African police earlier this month.

This was after Ms Campbell told the war crimes trial of ex-Liberian President Charles Taylor that she handed them as a donation to Mr Ractliffe after she was given them by two unidentified men after a 1997 charity dinner.

The prosecution says they were ‘blood diamonds’ from Mr Taylor.

Prosecutors called Ms Campbell to help prove Mr Taylor traded in illegal diamonds to arm Sierra Leone rebels. Mr Taylor was also an architect of Liberia’s civil wars.

The Nelson Mandela Children’s Fund yesterday said that Mr Ractliffe will leave its board this month.

In a statement, the Children’s Fund said Mr Ractliffe regretted not having informed other officials about receiving the three uncut diamonds earlier, “and acknowledges that had he done so, he and the board could have found a better and lawful way to manage the situation.”

It added Mr Ractliffe had apologised “for the anxiety and possible reputational risk his conduct may have caused”. The fund said he would not seek re-election in a board vote scheduled later this month and would resign from the board of the fund’s US affiliate.

Mr Ractliffe, a respected businessman, has said he kept the stones and did not report them to authorities in a bid to protect the reputations of Mr Mandela, Ms Campbell and the charity, of which he was a founder. It is illegal in South Africa to possess a rough diamond because of possible links to conflict zones, money-laundering and other crimes.