On most issues, we know where Mandela stood and how his thinking developed over the years. And, whatever we thought at the time, we're all Mandelistas now, or so the waves of tributes seem to suggest. But as to what he thought of Mrs Thatcher and her attitude to apartheid, there's little agreement. How much did he think she contribute to his release from prison in 1990? Could she have hastened it?
The story is clouded by much bluster at the time from the Tory back benches, many of whose occupants regarded anyone calling themselves a freedom fighter as beyond the pale, politically. An opinion article in the Daily Mail on the day of the concert to mark Mandela's 70th birthday in 1988 encapsulated their views: "The ANC and its leader Nelson Mandela have no more claim to be saints or heroes than do the Provisional IRA with their lynch mobs and car bombers." In the mid-1980s, Thatcher herself had described the African National Congress as a "typical terrorist organisation" and – in defiance of many among the black South African opposition –refused to apply more than minimal sanctions against apartheid.
Yet, fittingly or otherwise, the question was not black and white. On Friday night, Lord Renwick, Britain's ambassador to South Africa at the end of the apartheid era, told Newsnight viewers: "I was her envoy to Pretoria. My instructions were extremely clear – to get Mandela out of jail. As long as Botha [the hardline president from 1984 to 1989] was there we had no chance. But when de Klerk took over – he was a friend of mine and an admirer of hers. At midnight the night before he made his speech unbanning the ANC, he telephoned me and said you can tell your PM she will not be disappointed." Lord Renwick said Thatcher felt tougher sanctions would do more harm than good to the economic interest of South Africa's black people.
Margaret Thatcher's biographer Charles Moore is in no doubt as to where Thatcher's instincts lay. He denies she ever called Mandela a terrorist, and that from 1984, when she first met Botha, she "put pressure on him to release Mandela". "She wanted an orderly transition to majority rule" and knew Mandela was essential to that aim. She even wrote to Ronald Reagan expressing the hope that he be released. Mandela rejected freedom with conditions, writes Moore, but she "kept up the pressure, in public, in private, and sometimes in secret. Indeed, the release of Mandela was the strongest and most specific of all her demands."
Mandela's eventual release, after the change in the presidency, came with the help of Thatcher's persuasion, he says. "Her voice proved the most persuasive."
Lord Renwick says the British had worked intimately with Mandela, even during his time in prison, and that he knew exactly how British strategy was working. And when, after Mandela's release, he planned to meet Mrs Thatcher in April 1990, Mandela was prevented from doing so by the ANC hierarchy, according to documents released three years ago. He had wanted to explain to her why the ANC was so critical of her policy on sanctions, but his advisers prevented any engagement with her, at which he was said to be "furious".
The pair eventually did meet three months later. After that, Mandela said: "She is an enemy of apartheid… We have much to thank her for." At that meeting, their first, according to Renwick, he impressed her hugely, although she warned him about what she regarded as his wilder economic plans. He thanked her for everything she had done to secure his release.
Were his thanks sincere? They had every reason to be, according to her supporters. But here the political divide opens up. Others say Mandela had little choice in the circumstances but to express gratitude, and that, underneath, he shared the ANC's anger with her refusal to toughen sanctions.
On one reading, this is an argument about means against ends. Maybe both sides wanted the same thing, but disagreed on how to achieve it.
Many campaigners disagree, saying that Thatcher never showed the conviction to end apartheid that she showed in other areas, and that history is being rewritten.
One veteran of the anti-apartheid struggle is Helao Shityuwete, now 79, who was imprisoned on Robben Island with Mandela. He cites the much proclaimed "Wind of Change" speech by UK prime minister Harold Macmillan in 1960, which recognised the need for decolonisation. Speaking exclusively to The Independent on Sunday, he said yesterday: "We all wanted the Wind of Change in Africa to go on blowing until Mandela was released. But it stopped blowing when Thatcher and Ronald Reagan came in. They were more interested in fighting the Soviet Union than in fighting apartheid."
Maybe so, but did Thatcher have no influence on getting Mandela released? "No, we know de Klerk had spoken to Afrikaners beforehand. He had already agreed it was time to talk to Mandela. She didn't contribute at all." So why had he expressed thanks? "It was the politics of the time. He had to be polite and diplomatic, but he felt very betrayed indeed."
Another campaigner, Tom Minney, formerly of the Namibia Support Committee, says Mandela's concern would have been on the bigger picture, not just his own freedom. "In diplomacy, what's significant is often what they don't say and don't thank you for."
Thatcher's surprise arrival in March 1989 in Namibia, then struggling to break free from South Africa, also divides opinion. Some see her as the saviour of the situation, with her bringing pressure to minimise South African violence against insurgents and helping bring about independence a year later. Others say her presence effectively gave the security forces a licence to the bloody killing of a number of Namibian nationalists in the north, angry at Pretoria's continued refusal to allow independence. "She nearly prevented Namibia getting its freedom," says Shityuwete. "We had no option but to fight back after that." In the event, the UN became more heavily involved (at Thatcher's insistence) and independence came in 1990.
Campaigner Peter Hain is in no doubt. "I am astonished at the bare-faced effrontery of these Tories who were sucking up to the apartheid leaders. The economy did for apartheid and sanctions were decisive, particularly the very sanctions Thatcher hadn't wanted. The white business community had done very well out of apartheid, but after loan sanctions, by the Americans, came in, they demanded change."
So why did Mandela express his thanks to Thatcher like that? "He had such a generous spirit," says Hain, "that maybe there was some polite exchange. But he specifically told me, in private, how angry he was with those who had opposed sanctions and who then claimed credit for the transformation."
The phoney consensus on Mandela, on this at least, is at an end.
Video: House of Commons pays tribute to Nelson Mandela