LONDON (Reuters) - Simon Mann, a British mercenary jailed for plotting against the government of Equatorial Guinea, has said South Africa tacitly supported a failed 2004 coup in the oil-rich African nation.

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."