As South Africa celebrates the 20th anniversary of Nelson Mandela's release from prison, David Cameron has come under pressure to apologise for his visit to the country during apartheid.
It emerged in a biography last year that the Conservative leader visited South Africa as the guest of anti-sanctions lobbyists in 1989, when Mandela was still in jail.
The senior Labour MP Richard Caborn and the former TUC general secretary Norman Willis have written to the Tory leader to demand a public apology.
"Your trip, paid for by lobbyists against sanctions, was a long time ago," they wrote.
"But it was then, and is now, a question of values and judgment. Since the details of this trip became public, you have refused to comment on it, refused to explain why you had to keep it quiet and refused to apologise for your actions. We hope that on the anniversary of Nelson Mandela's release, you will set the record straight and do what is right."
A Conservative spokesman said at the time that the visit was a chance for Mr Cameron to "see for himself" what conditions in South Africa were like, and noted that he met anti-apartheid campaigners while in the country.
Cameron has previously admitted that his party was wrong to oppose sanctions against the apartheid regime and has repudiated Margaret Thatcher's description of Mandela's African National Congress as "terrorists".
