Mann, who was released from prison earlier this month, told the BBC he believed that the operation had the unwritten consent of South African intelligence.
“South Africa wanted to be in,” he said, according to extracts of an interview to be broadcast on Tuesday. “In fact, I was told: ‘Get on with it.’”
“Because, if they are very good friends of the new government, it would be of great benefit to South Africa because they know perfectly well that billions of dollars are at stake,” 57-year-old Mann said.
Educated at Eton, Britain’s top private school, the ex-special forces officer was arrested in Zimbabwe along with 70 other mercenaries en route to Equatorial Guinea aboard a plane.
Extradited to Equatorial Guinea, he was sentenced in July 2008 for conspiring to topple President Teodoro Obiang Nguema Mbasogo. He was pardoned on health grounds, having served just over one year of a 34-year sentence.
During his trial, Mann portrayed himself as a pawn of international businessmen he said were trying to seize power and named the son of former British Prime Minister Margaret Thatcher as being involved — an allegation Mark Thatcher has denied.
In the BBC interview, Mann said he got on well with Mark Thatcher, at one point his neighbour in South Africa, describing how Margaret Thatcher would come and stay in a cottage in the garden of her son’s house.
“I always sat next to her at dinner parties,” he said. “She liked me. We even went on holiday together.”
Mann, who said that from his point of view the purpose of the coup was to make money from the oil-rich country, said he wanted Mark Thatcher as an investor in the plot, and that he had told him precisely what the operation was.
Discussing some of his early plans for the coup, Mann said he had also considered an assassination and a guerrilla war, but these options had been discarded.
He said had been unhappy with aspects of the final plan but was under pressure from unnamed backers to get the coup over.
“I thought there was quite a good chance I was going to die, because I knew that far too many people knew about the operation,” he said, adding that he should have had the courage to halt the plans but failed to.
On Sunday, Equatorial Guinea’s President Obiang looked set to win an election landslide, extending his 30-year rule.