By politics.co.uk staff
David Cameron has been asked to apologise for a visit to South Africa to campaign against sanctions on the anniversary of Nelson Mandela's release from prison.
The Conservative leader flew to the country as the guest of anti-sanctions lobbyists in 1989, while the future president was still in prison.
Mr Cameron has already acknowledged his party's "mistakes" on the issue while visiting in 2006.
Labour MP Richard Caborn and ex-TUC general secretary Norman Willis, a prominent anti-apartheid campaigner, 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 judgement.
"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."
Tory spokespeople insist Mr Cameron flew to the country to see conditions and that he met with opposition politicians while there.
Margaret Thatcher's persistent commitment to South Africa, and her attempts to prevent any attempt at sanctions on it, was a major cause of anger towards the Tory leader in the 1980's.