Nelson Mandela's name was not raised once in an official meeting between Margaret Thatcher and South Africa's prime minister in 1984, records showed, re-opening the debate into how much she pushed for his release from prison.
P. W. Botha was invited to talks with the Thatcher at the British prime minister's Chequers country residence to discuss South Africa's policy towards its black population, as the apartheid regime sought to emerge from its international isolation.
The record of that meeting, released 30 years later under secrecy rules, showed that Thatcher pressed Botha on the issue of apartheid but Mandela's name did not come up during the official talks.
Thatcher chose instead to raise the issue during a shorter private discussion the two leaders had beforehand, where no official note-takers were present.
The newly declassified official records show that the British government confirmed that Mandela's imprisonment was raised at a short "tete-a-tete", but that Thatcher made little progress with Botha.
In a note about the 40-minute private meeting sent to the Foreign Office on June 2, 1984, Thatcher's advisor John Coles wrote: "The prime minister said afterwards that Mr Botha had stated that it was never possible for South Africa to satisfy international opinion.
"She took the opportunity to raise the case of Nelson Mandela.
"Mr Botha said he noted the prime minister's remarks, but that he was not able to interfere with the South African judicial process."
But in the broader, four-hour meeting where official minutes were taken, Thatcher omitted the leaders' disagreement over anti-apartheid hero Mandela -- despite prior guidance from the Foreign Office to make the point.
In a briefing paper written by the Foreign Office for the prime minister's office ahead of the meeting, it was suggested that Thatcher include Mandela's release from prison as a "point to make".
In a statement to the House of Commons, the lower house of parliament, after the meeting, Thatcher said: "On the internal situation in South Africa, I expressed our strongly held views on apartheid.
"I told Mr Botha of my particular concern at the practice of forced removals (of the black population) and raised the question of the continued detention of Mr Nelson Mandela."
In her 1993 memoir, "The Downing Street Years", Thatcher said that in the meeting with Botha, she raised the case of Mandela, "whose freedom we had persistently sought".
He was finally released "after all the years of pressure, not least from me", she wrote.
The revelations come after the historical approach of the Conservatives -- the party of Thatcher and current Prime Minister David Cameron -- to Mandela's African National Congress party came under scrutiny after the peace icon's death last month.
Reminded that Thatcher branded the ANC a "typical terrorist organisation" during a press conference in 1987, a senior Conservative former minister, Norman Tebbit, said: "He was the leader of a political movement which had begun to resort to terrorism."
Cameron has in the past apologised for his party's approach to apartheid-era South Africa.
In 2006, he flew to South Africa to seek forgiveness from Mandela for "the mistakes my party made with the ANC and sanctions in South Africa".
Cameron said at the time that Thatcher had been wrong to brand the ANC "terrorists".