IN the summer of 2004, Sir Mark Thatcher returned home to South Africa as a wanted man. As he sauntered through customs in Cape Town, he was taken aside by an official and told the Scorpions, one of the country’s elite police units, wanted to talk to him.

The Scorpions — an anti-corruption division — were renowned for their fearless investigations of high-ranking officials and some of the country’s best-connected businessmen. Thatcher realised he was in a tight spot, facing the prospect of charges over his role in the botched coup attempt in Equatorial Guinea in March 2004.

It has now emerged that shortly after this airport encounter, he arranged a confidential meeting with a senior intelligence official in Pretoria on August 20. He was apparently ready to reveal what he knew about any coup plot to try to halt the Scorpions’ inquiries.

At first, it seemed his ploy had worked. The next day, he got a call and — according to his own account — he was told he had been accepted as a “nominated SASS [South African Secret Service] source”.

Four days later, Thatcher was arrested by the Scorpions at his suburban Cape Town home in an early morning raid. He was livid. The police and intelligence services just don’t talk to each other, he complained bitterly.

Adam Roberts, author of The Wonga Coup, who has confirmed in interviews with Thatcher that he was accepted as a South African intelligence source, said: “Thatcher felt he was very unfairly treated by the South Africans because he thought he had been accepted as an intelligence source. He felt he was singled out for harsh treatment while others got away more lightly.”

Roberts said during the interviews, Thatcher had joked that if he published any unflattering comments, he would need “a new dental surgeon”. He also said that if he identified him with the Equatorial Guinea plot, he would end up as “Mr Stumpy”, walking around on stumps for legs.

Thatcher last week admitted to The Sunday Times that he had met a foreign affairs official to discuss the coup plot in August 2004, but said he never suspected the man worked for the SASS. He denies trying to strike any deal or offering his services as an informant. He claims that at that time he had no reason to fear that he risked prosecution.

“I thought these guys were tough guys,” one South African source said last week. “Yet they were all squealing like canaries.They really rather let down the names of mercenaries.”

In January 2005, Thatcher was fined the equivalent of £265,000 for breaking South Africa’s anti-mercenary laws by providing funds for a helicopter for the operation. Thatcher denied knowing about the plot, but was given a four-year suspended jail sentence in a plea bargain.

Last week Thatcher’s murky role in the Equatorial Guinea affair — and his contact with South African intelligence services — came back to haunt him. After more than five years in jail, his erstwhile friend Simon Mann, a mercenary involved in the attempted coup, was finally allowed to go home.

As Mann, 57, a former SAS officer, set foot on British soil on Wednesday, he looked in fine fettle for a man who had been incarcerated in Black Beach prison, one of the most notorious in Africa. While inside, he had enjoyed privileges, including fine rioja wines and steaks cooked at a nearby hotel.

Times Recommends

• Please help: maimed children of war want their lives back
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president