The homecoming of Simon Mann

With its sweeping views over the Solent, Palladian architecture and 20 acres of Hampshire pasture, Inchmery House stands in stark contrast to the concrete prison cell in Equatorial Guinea which Simon Mann had, until yesterday, called home.

The Old Etonian and ex-SAS officer had expected to remain incarcerated in the notorious Black Beach jail until his 90th birthday. Last night he was on his way back to his £5m British country residence via a five-star hotel in the oil-rich west African country after being granted a pardon by the authoritarian leader he had tried to depose in a botched coup.

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Mann, 57, was released by President Teodoro Obiang Nguema, along with four others who had conspired to seize control of the tiny petro-state in 2004. Their failed attempt became known as the "Wonga coup" for its hugely lucrative ambitions and the alleged backing of a colourful cast of players that included Mark Thatcher and a Lebanese oil billionaire. Mann had stood to gain £9m if the coup had succeeded.

An Equatorial Guinean government spokesman said that Mann, who led a team of more than 60 battle-hardened South African mercenaries, had been released on "humanitarian grounds", citing his need for medical attention after a hernia operation last year. He had served less than two years of a 34-year sentence imposed last June.

The father-of-seven was met yesterday by his wife, Amanda, and sister, Sarah, after two months of secret negotiations. But when he touches down today on board a private jet, he will face a barrage of questions.

As well as meeting for the first time his five-year-old son Arthur, who was born shortly after his arrest in March 2004, Mann can expect a phone call from officers of Scotland Yard's counter-terrorism command. Police yesterday confirmed that an investigation is still ongoing into whether any offences were committed in Britain during the planning of the coup. It is expected that Mann, the scion of a brewing dynasty whose father and grandfather captained the England cricket team, will be questioned as a witness.

The Foreign Office said it had been told that the release was a personal decision by Mr Obiang, an autocratic ruler previously accused of cannibalism, who has ruled the former Spanish colony since 1979. Equatorial Guinea sits on vast petro-chemical reserves which make it sub-Saharan Africa's third largest oil producer and earn it £40m a day. Critics point out that despite such wealth, the country's population remains one of the most impoverished on the planet.

It is understood that the pardon was the result of a private deal between Mr Obiang and Mann under which the Briton pleaded guilty to leading the coup and provided a comprehensive account of the plot which portrayed him as an "accomplice" to a coterie of international businessmen who had acted with the tacit approval of the governments of Spain and South Africa.

During his testimony, Mann implicated Mr Thatcher, the son of the former prime minister, as one of five "managers" of the plot along with Eli Calil, a Lebanese-Nigerian oil trader based in London. Mr Thatcher was convicted in South Africa in 2005 of unwittingly helping to finance the plot when he paid £140,000 for a helicopter.

Bungled coup: Lines of inquiry

* Will Simon Mann stand by his testimony to a court in Equatorial Guinea that Mark Thatcher was part of the "management team" for the coup?

* Will the mercenary also continue to insist that Ely Calil, the reclusive Lebanese oil billionaire, was "the Cardinal" – the powerful businessman who originated the coup plot?

* Did the CIA blow the whistle on the coup attempt to protect the interests of American oil companies?

* Did the Spanish authorities give tacit approval to the plan to replace President Obiang with Severo Moto, an opposition leader in exile in Madrid?

* What knowledge did Britain have of the plans for the coup and did London seek to warn the Obiang regime of what was happening?