British detectives are using new anti-terror laws to investigate the failed plot to overthrow the government of Equatorial Guinea, it has emerged.
Officers from Scotland Yard's elite SO15 Counter Terrorism Command are probing the 2004 conspiracy at the request of the West African state, according to a report in The Mail on Sunday.
Details of "Operation Antara" emerged as former SAS officer Simon Mann awaits sentence for his involvement in the attampted coup, after his trial in Malabo finished on Friday.
The Metropolitan Police team are believed to be investigating three prominent figures already implicated in the plot – reclusive oil tycoon Ely Calil, Sir Mark Thatcher and property dealer Greg Wales.
The latest development in the investigation came as a former Foreign Office minister denied that he was aware of the plot, despite claims that Mr Mann was unofficially warned by Britain to cease his mercenary activities.
Chris Mullin, who was Foreign Office minister of state with responsibility for Africa from June 2003 to May 2005, said: "I had no advance knowledge of the plot until Simon Mann was arrested. I can't speak for anyone else, but I was the minister in charge at the time, and I knew nothing about it ... There is no reason why the British government necessarily would have intelligence on Equatorial Guinea, as we don't have an interest in it."
Similar denials were issued at the time of the thwarted coup in March 2004 by the Foreign Office and Jack Straw, then Foreign Secretary. But later the same year Mr Straw admitted in a parliamentary answer that Britain had been told of the plot more than a month before it was put into action.
Sources close to the affair say Mr Mann later received a warning that Britain was aware of the conspiracy, and that he should "hang up his boots".
The question of what Britain knew about the coup plan, and what action it took, has arisen in the wake of Mr Mann's evidence in court in Malabo, Equatorial Guinea's capital. The Old Etonian faces a sentence of up to 32 years this week after admitting his role in the plot to overthrow President Teodoro Obiang Nguema and replace him with Severo Moto, an exiled opponent. This, he claimed, had the semi-official approval of both the Spanish and South African governments.
He was jailed in Zimbabwe after being arrested at Harare airport, where he took delivery of a consignment of arms and met more than 100 ex-soldiers on a flight from South Africa.
Yet even though the 55-year-old ex-officer implicated Sir Mark Thatcher and other Britons in his evidence, he said nothing about the British government's position.
The country's Attorney General, Jose Olo Obono, who prosecuted the case against Mr Mann, told this paper in 2004 that Britain and the US were "fully aware" of the plot. "We received warnings from South Africa, Zimbabwe and Angola, but nothing from Britain or America," he said. "There are indications that they, like Spain, were prepared to recognise a Severo Moto government."
A source closely acquainted with the affair said Mr Mann, who holds dual British and South African citizenship, was aware Britain was the only country he could realistically head for if and when he left Equatorial Guinea. In prison in Zimbabwe he had turned down the chance to be extradited to South Africa.
How do the allegations made in court by Simon Mann measure up?
Spain knew and approved of the coup plot
Mann said coup plans had been rushed through in March 2004 because the conservative government had promised immediate diplomatic recognition, and it was feared that the then Prime Minister, Jose Maria Aznar, would lose to the Socialists in the election. Spain's Foreign Ministry denied the claim.
South Africa, up to the level of President Thabo Mbeki, also gave a "green light" for the plot
This was the first time anyone had heard such an allegation, which South Africa angrily denied last week. Although South Africa warned Malabo of the plot in March 2004, Equatorial Guinea is said to be aggrieved at what it sees as lack of South African co-operation since.
Mark Thatcher "was not just an investor" in the plot, "he came completely on board and became a part of the management team"
If so, it is surprising the mile-wide paper trail did not seem to carry his name. Thatcher admitted involvement in the plot in a South African court, and received a £266,000 fine and four-year suspended sentence.
London-based oil trader Ely Calil was "the overall boss" of the mission
Calil has denied involvement, but made no further comment. In court Mann said he had taken Thatcher to Calil's London home.