Simon Mann, the Old Etonian mercenary, has placed Sir Mark Thatcher right at the heart of the plot to overthrow the President of the oil-rich Equatorial Guinea in 2004.

In electrifying testimony before a court in the tiny West African state yesterday, Mann flatly contradicted Sir Mark’s insistence that he knew nothing about the attempted coup d’état and gave money unwittingly.

Mann said that he recruited the former Prime Minister’s son and took him to London to be vetted by Ely Calil, the Lebanese-Nigerian tycoon whom he identified as the “boss” of the whole operation. After that, he said, Sir Mark was “not just an investor. He came on board completely and became part of the management team”, attending many meetings. He named Sir Mark as one of five men “in charge of the operation”.

Sir Mark struck a plea bargain with South African prosecutors in 2005. He admitted paying $275,000 (£140,530) for a helicopter but claimed that he thought it was to be used as an air ambulance. He was fined £266,000, received a four-year suspended sentence, and now lives on an exclusive estate in Spain while Mann is in the infamous Black Beach jail in Malabo.

José Olo Obano, the Attorney-General of Equatorial Guinea, said that he would seek the extraditions of Sir Mark and Mr Calil. In March Mr Calil denied any link with the plot.

In four hours of testimony Mann also claimed that the attempted coup was in effect an “official operation” sanctioned by the Spanish and South African governments, and that even President Mbeki knew of it.

He said that the Pentagon, the CIA and the US oil companies who have invested heavily in Equatorial Guinea were sounded out, and all signalled that a “well-conducted change of government would be welcome”. However, he declined to implicate the British Government, saying he was “amazed” to learn later that it had been aware of the plot.

Mann spoke calmly, but it was the testimony of a man fighting to avoid three decades in an African prison. The former SAS officer lost his composure only when the judge asked whether a 30-year sentence was justified. “I don’t agree with that. No. Please,” he replied.

He ended his testimony with an abject apology, adding: “I’m also very happy that we failed . . . especially now that I am here and have met some of you. And I think that the people who were seriously involved and have not faced justice should do so.”

Mann — who stood to make at least $15 million (£7.7 million) if the coup succeeded — claimed that he agreed to remove President Teodoro Obiang Nguema, reputedly one of Africa’s most corrupt and brutal dictators, “for the money yes, but also because it was the right thing to do”.

He said that he rejected the idea of assassinating Mr Obiang, and that he and his 80 fellow mercenaries were to land in Malabo straight after a palace coup, merely to guard Severo Moto Tsa, the exiled opposition leader who would replace the ousted President.

“When we arrived we would not be shooting, we would be shaking hands,” he said. Plan B — taking Malabo by force — would only kick in if the palace coup failed. Even then there was no plan to “erase people”.

Mann said Mr Calil and Mr Moto repeatedly assured him that José Maria Aznar’s conservative Government in Spain was “100 per cent behind the coup”, would immediately recognise Mr Moto’s administration, and send Civil Guards to help to keep order.Spain denied this last night.

Mr Mbeki’s spokesman also denied that the South African President or his Government knew of the plot.

The trial continues.

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