How former PM's son became embroiled in mystery of plot to oust brutal despot

A crumbling African state with a fabulous fortune in oil, a murderous dictator accused of cannibalism, and a planned coup allegedly involving Sir Mark Thatcher and mercenaries led by a former SAS officer.

These are the extraordinary ingredients in a tale of intrigue, violence and realpolitik, catapulted to international headlines yesterday by the arrest of Baroness Thatcher's son at his £2m home in Cape Town.

At its heart lies an alleged plot to overthrow Teodoro Obiang Nguema, the President of Equatorial Guinea, a country deeply impoverished, but which is also Africa's third-largest oil producer. He was to be eliminated and replaced, it is claimed, by a government led by an exiled opposition leader, Severo Moto Nsa, who would reward those who financed the mercenaries with lucrative oil contracts.

A central figure is Simon Mann - an Old Etonian former soldier and scion of the Watney brewing empire whose father once captained England at cricket - who is now on trial in Zimbabwe, accused of being the leader of the plot.

His contacts in Britain were said to include Sir Mark, and Ely Calil, a London-based oil trader who made his fortune in Nigerian oil. In June 2002, Mr Calil was questioned by French police investigating payments of millions of pounds in commission by the French oil company Elf Aquitaine to Sani Abacha, the former dictator of Nigeria.

Mr Calil, of Lebanese background, is a former financial adviser to Jeffrey Archer. The disgraced peer and former Tory deputy chairman is alleged to have paid Mr Mann £80,000, but he has denied knowledge of any coup plot.

The oil trader lives in a £12m house in Chelsea and has several other properties that he rents out. Peter Mandelson, while Northern Ireland Secretary, was a tenant, renting a £500,000 apartment in Holland Park. But there is no suggestion Mr Mandelson has other connections to Mr Calil.

Mr Mann, who has been held at Chikurubi prison, outside Harare, for five months, pleaded for help from Sir Mark, who inherited the baronetcy of his late father Denis's title, and is a neighbour of Mr Mann in the exclusive Cape Town suburb of Constantia.

The accused mercenary leader also asked for aid from David Hart, another Old Etonian, a businessman with right-wing views who was an adviser to Margaret Thatcher during the miners' strike and later played a part in Michael Portillo's bid to become Conservative leader. Representing both the men, in public relations, is Lord Bell, who once fulfilled a similar function for Lady Thatcher.

In a letter from his cell on 31 March, to his wife Amanda and his legal team, Mr Mann, 51, said: " Our situation is not good and it is very URGENT. They [the lawyers] get no reply from Smelly and Scratcher [who] asked them to ring back after the Grand Prix was over! This is not going well. I must say once again: what will get us out is MAJOR CLOUT. We need heavy influence of the sort that "... Smelly, Scratcher ... David Hart, and it needs to be used heavily and now. Once we get into a real trial scenario, we are f....d". South African colleagues of Mr Mann have confirmed that Scratcher is Mark Thatcher, and Smelly is Mr Calil.

Lord Bell's organisation said neither Sir Mark nor Mr Hart had any knowledge of the alleged coup plot, and had merely been asked for help by Mr Mann. Imran Khan, the London solicitor who has appeared in several high-profile cases of racism, including the Stephen Lawrence inquiry, is acting for Mr Calil. He said: "We will vigorously defend the allegations, which are totally without foundation."

Mr Mandelson said: "I have no knowledge of any coup and he [Mr Calil] has not sought my advice on it." He has refused to discuss in detail his relationship with the Lebanese businessman but said he had paid "the proper rent personally" for the apartment, and that it has been for less than a year.

Mr Calil is being sued in the High Court in London by the government of Equatorial Guinea for being allegedly seeking to "maliciously overthrow ... the lawful government of Equatorial Guinea by acts which are crimes in England..." Also named in the court documents are Mr Mann, Mr Moto, who is based in Madrid, and Greg Wales, a businessman in London.

President Obiang, who has been in power for 30 years, is no stranger to legal attention. A US Senate investigation into money-laundering involving a Washington financial house, Riggs Bank, concluded that he and his family have "misappropriated" at least £35m from national oil revenues.

Opposition groups claim his secret police routinely tortured and killed political detainees, and he ate human flesh, including testicles of executed prisoners, in the belief that it gave him martial prowess.

Equatorial Guinea, has a poverty-stricken population of 500,000 but it is blessed with vast and largely untapped oil resources. is said to have been viewed as a country to be exploited. It is alleged that Simon Mann was chosen as the man to head such an operation.

The former soldier had plenty of experience of clandestine military action in Africa. Eleven years ago, he set up a private military company, Executive Outcomes, with an associate, Tony Buckingham, which made millions protecting oil installations in Angola from Unita rebels. It also fought for the Sierra Leone government against rebel forces, and one of its subsidiaries, Sandline International, set up with a former Scots Guards officer, Lieutenant Colonel Tim Spicer, was at the centre of the so called "arms to Sierra Leone" scandal in the late 1990s.

Alleged confessions extracted in Zimbabwe and Equatorial Guinea claimed secret meetings were held in South Africa, Spain, and England, to plan a rising in the Guinean capital, Malabo, which would coincide with the arrival at the airport of heavily armed mercenaries. President Obiang was either going to bundled off to Spain, the former colonial power, or killed, according to confessions by men arrested in Malabo and accused of being the mercenaries' advance party.

But Ronnie Kasrils, South Africa's Intelligence Minister, disclosed that his service tipped off the Zimbabwean authorities as the mercenaries took off for Harare to collect weapons on their way to the Guinea capital.

Mr Mann and 66 South Africans, many of them former members of special forces, were arrested when their chartered Boeing 727 touched down at Harare on 7 March. The following day 15 others, including Nick du Toit, a former South African soldier, were picked up in Malabo. In an alleged confession, Mr Mann said he met Mr Calil in London, and he had offered to introduce him to the exiled opposition leader Mr Moto.

Mr Mann also said he was introduced to another exiled activist who claimed he was forced to watch while President Obiang raped his wife.

At the opening of the case in Harare, Mr Mann and his fellow defendants pleaded guilty to paying £100,000 in attempting to acquire weapons. But they insisted that they were simply organising security for a diamond mine in the Democratic Republic of Congo.

In court in Malabo, Mr du Toit claimed Sir Mark was not involved in the plot but they had met in the months beforehand.Mr du Toit said Sir Mark was interested in buying military hardware for "a mining deal in Sudan".

There were reports that Equatorial Guinea was seeking Sir Mark's extradition. But, after seeing yesterday's television footage of the former British prime minister's son being marched off to a cell, the Guinean Justice Minister, Ruben Mangue, was magnanimous. His government, he said, was in no hurry. "Let's first give an opportunity to the South African authorities and the South African legal system to handle the situation."