British intelligence operatives "posed as birdwatchers" to spy on Nelson Mandela's ANC hideout before he was arrested, it has been claimed.
Denis Goldberg, a white communist and ANC bomb maker who was detained in the surprise raid on Liliesleaf Farm by South African police on July 11 1963, said he believed a number of intelligence agencies including the British and Americans were monitoring.
"We believe that there was a British intelligence agent in the nearby caravan park," he told an audience at a 50th anniversary event to commemorate the raid. "Everyone thought he was a birdwatcher because he would climb up a telegraph pole with binoculars every day.
"But I think we were the birds he was watching."
Mandela and fellow ANC leaders used Liliesleaf, the home of a white sympathiser, to plot their armed rebellion against the apartheid government in the early 1960s.
Mandela, who had been forced underground because of his illegal political activities, was arrested in August 1962 at a police roadblock in KwaZulu Natal.
Ten of his contemporaries, including Mr Goldberg, Walter Sisulu, Govan Mbeki and Ahmed Kathrada, were arrested at Liliesleaf almost a year later with documents which saw all of them, including the already detained Mandela, prosecuted for sabotage.
Mandela went on to serve 27 years in prison before becoming South Africa's first black, democratic president in 1994.
The CIA has long been suspected of providing information that led to Mandela's detention.
But the possible involvement of the British security services has rarely been mentioned.
Mr Goldberg's claims are backed by Nicholas Wolpe, the son of another Liliesleaf detainee, Harold Wolpe, who now runs Liliesleaf as a visitor centre and has researched the events leading up to the raid extensively.
"A woman living near to the caravan park was a great birdwatcher and she reveals always seeing two guys up a telephone pole with binoculars," he said. "She only put two and two together after the raid."
But he added that none of the Liliesleaf arrestees thought the British gave them away.
"No British name crops up in the research I have done. If the British were monitoring what was happening, which I think they were, they were being very discreet about it," he said.
Ahmed Kathrada remains adamant that neither British nor American help prompted the Liliesleaf raid. "One of our own was arrested and detained, and he gave us up," he said.
Professor Sir Bob Hepple QC, a white South African also arrested at Liliesleaf who fled to England when he was released on bail, claimed there was some intelligence traffic between the two countries.
"We know that MI5 and the South African police collaborated," said Sir Bob, a Cambridge University law professor.
"When I arrived in Britain and had to claim political asylum in December '63, I was interviewed by a Home Office man who was clearly MI5. It was clear he knew things he could only have got from the South African police."