South African police arrested the son of former British Prime Minister Margaret Thatcher yesterday on suspicion of involvement in a coup plot in oil-rich Equatorial Guinea, police sources said.

A spokesman for the FBI-style Scorpions unit said that “the son of a prominent former British politician” had been arrested after a search and seizure operation at a Cape Town residence.

Police sources said the suspect was Mark Thatcher, now a businessman who maintains a home in Cape Town. He was expected to appear in court lateryesterday.

Scorpions spokesman Makhonsini Nkosi said the arrest was part of a probe into what officials say was a plot to topple President Teodoro Obiang Nguema Mbasogo of Equatorial Guinea, sub-Saharan Africa’s third largest oil producer.

“We are investigating him on charges of contravening the Regulation of Foreign Military Assistance Act. This is in relation to the possible funding and logistical assistance in relation to the attempted coup in Equatorial Guinea,” Nkosi said.

British High Commission spokesman Nick Sheppard said the Commission was checking reports of Thatcher’s arrest. “If Mr. Thatcher has been arrested we will offer him the normal consular assistance we offer to any British national who is arrested in SA,” he said.

Two groups of men, including a number of South Africans, are being tried in courts in Equatorial Guinea and Zimbabwe on charges of acting as mercenaries in connection with the plot.

Thatcher moved to Cape Town in 1996 from the United States, where he was involved in several security-related businesses.

Local media have said that he is close to Simon Mann, the former British special forces member regarded as the leader of the Zimbabwe group of suspected mercenaries, who were arrested in March when their plane landed in Harare on what officials said was a trip to join co-conspirators in Equatorial Guinea.