The son of former British prime minister Margaret Thatcher, an ex-race car driver whose business career has been dogged by accusations of questionable arms deals and shady ventures, was charged Wednesday with helping to finance a foiled coup plot in oil-rich Equatorial Guinea.

Mark Thatcher, 51, was arrested at his Cape Town home and charged with violating the country's Foreign Military Assistance Act.

"We have evidence, credible evidence, and information that he was involved in the attempted coup," said Sipho Ngwema, a police spokesman. He said South Africa would not allow itself to become "a springboard for coups in Africa and elsewhere."

Authorities in several African countries announced in March that they had foiled an attempt to overthrow the president of Equatorial Guinea, Teodoro Obiang Nguema, who has been widely accused of torture and other abuses while ruling a nation that has become sub-Saharan Africa's third oil producer.

Magistrate Awie Kotze placed Thatcher under house arrest and gave him until Sept. 8 to post bail of $300,000.

Outside court, Thatcher's attorney said he was arrested on suspicion of providing financing for a helicopter linked to the coup plot.

"Mr. Thatcher is not guilty of any allegations," said his attorney, Alan Bruce-Brand. "He has nothing to hide and is already cooperating with authorities."

There was no immediate reaction from Thatcher's mother.

Police raided Thatcher's home in the upscale suburb of Constantia shortly after 7 a.m. Investigators searched his records and computers.

Hours later, Thatcher was driven away in a police vehicle. But his court appearance was delayed when his shoes, jacket and cell phone were stolen while he waited in a crowded holding cell, according to a court official who witnessed the attack. Police recovered the items.

Equatorial Guinea put 19 people on trial Monday in the alleged plot. Another defendant died in custody under suspicious circumstances. Seventy other suspects accused of being mercenaries are on trial separately in Zimbabwe.

At the trial in Equatorial Guinea, a lawyer representing the government said on condition of anonymity that the country would be interested in Thatcher's extradition.

"The president has indicated that applications for the extradition of any person involved could well be pursued. It is expected that all steps will be taken to bring to justice those responsible, however highly placed they may be," the lawyer said.

One of the defendants testified that Thatcher met with Simon Mann, the alleged ringleader of the plot, in July 2003. Nick du Toit, a South African arms dealer, said Thatcher expressed interest in buying military helicopters for a mining enterprise in Sudan, but described the meeting as a "normal business deal" unrelated to the alleged coup plot.

Mark Thatcher, second from left, son of former British prime minister Margaret Thatcher, is escorted by police in Cape Town, South Africa.