Sir Mark Thatcher's is once again haunted by his murky past, which includes involvement in a bungled coup in central Africa, with last week's release of his co-plotter Simon Mann.

A Sunday Times report revealed Margaret Thatcher's son had frantically offered to become an informer for South African spy agencies to avoid being prosecuted for his involvement in Equatorial Guinea's 'Wonga coup'.

Dark warnings by 57-year-old Mann, who spent five-and-a-half years in two of the world's most notorious jails, that he has not forgiven betrayals and would help bring him to justice has rekindled interest over Sir Mark's role.

Evidence of his role has only been traced back to providing finance for the plot and hiring a helicopter for the coup.

Mann, a mercenary, maintains he and Ely Calil, a wealthy London-based Lebanese businessman, were key figures in the plot — allegations which both men deny.

Sir Mark was arrested four days after offering to become a spy by the Scorpions, an anti-corruption unit known for its fearless investigation of high-ranking officials. He was released on bail of 2 million rand and spent a period of time under house arrest before returning to London.

“Thatcher told me [in an interview] that four days before his arrest he had been accepted as an intelligence source by SASS [South African Secret Service]. He blames his arrest on a lack of communication between various government departments,” the daily quoted Adam Roberts, an Economist journalist and author of The Wonga Coup, a book about the plot, as saying.

Roberts said during the interviews, Sir Mark had joked that if he published any unflattering comments, he would need 'a new dental surgeon', among other thinly-veiled threats.

Thatcher now denies any of the former admissions of the desperate deal, claiming that he does not recall having told Roberts that he was a 'nominated SASS source', as he had not realized the man he met was an intelligence agent at that time.

Mann, serving a 34-year prison term, was pardoned last week and released from jail. He says he has been in contact with Scotland Yard detectives investigating British links to the plot.

The botched plot was simple; in March 2004, former SAS official, Mann, Nick du Toit and three other South African mercenaries were planning to fly into the former Spanish colony in a plane loaded with arms to replace Obiang with an exiled opposition activist called Severo Moto.

The plotter had finance, the assistance of 50 former members of South Africa's now disbanded Battalion 32, and the tacit approval of at least three governments, most notably the Spanish.

Zimbabwe intercepted the plane in March at Harare airport and threw Mann and his fellow conspirators into jail before handing them over to Equatorial Guinea.

ZHD/AKM