Mark Thatcher, the son of former British Prime Minister Margaret Thatcher, was planning to leave his home in South Africa for the United States when he was arrested in connection with an alleged coup plot, a police spokesman said Thursday.

Thatcher was arrested Wednesday and charged with helping to finance what authorities say was a foiled plot to overthrow the president of oil-rich Equatorial Guinea (search) in March.

Police in South Africa, where Thatcher has lived since 1995, have information that the 51-year-old businessman had put his $3.3 million home up for sale and had booked flights for his American wife and two children to Dallas, police spokesman Sipho Ngwema said.

Thatcher's two children had already been enrolled in schools in Dallas.

"The flights were booked for Monday and we believe Thatcher would have followed them. If you move your family and sell your property it follows that you would be leaving the country, too," Ngwema said.

Thatcher is under house arrest until he posts bail of $300,000, set after he was charged with violating the country's Foreign Military Assistance Act.

He is alleged to have financed the purchase of a helicopter to assist in the coup plot in Equatorial Guinea.

In a statement released Thursday, Thatcher maintained his innocence, the South African Press Association reported.

"I have been and am co-operating fully with the authorities in order to resolve the matter. I have no involvement in an alleged coup in Equatorial Guinea and I reject all suggestions to the contrary," the statement said.

Thatcher's lawyers were not immediately available for comment.

The former race-car driver lived in Texas once before. He moved to Dallas in April 1984 after a controversy over reports he represented a British construction firm that won a $600 million contract in Oman while his mother was there on a trade-boosting trip in 1981.

While living in Dallas, he settled a civil racketeering lawsuit for an undisclosed sum. He also faced charges from the Internal Revenue Service over his role with a Dallas-based home security company that went bankrupt.

Thatcher moved his family to South Africa in 1995 after business troubles in the United States.

Speaking at a media briefing Thursday, British Foreign Secretary Jack Straw would not be drawn in on the matter.

"Mark Thatcher, as a British citizen, is entitled to the same consular assistance as any other British citizen. He is also entitled, as every British citizen is, to that consular assistance being confidential," he said.

Authorities in several African nations announced in March that they had foiled an attempt to overthrow President Teodoro Obiang (search) of Equatorial Guinea, who is widely accused of torture and other abuses while ruling the continent's third-biggest oil-producing nation.

Equatorial Guinea put 19 people on trial Monday in the alleged plot. Seventy suspected mercenaries are on trial separately in Zimbabwe.

The alleged ringleader, former British special forces soldier Simon Mann (search), was among those arrested. At the Equatorial Guinea trial, a defendant testified Wednesday that Thatcher met with Mann in July 2003.

Nick du Toit (search), a South African arms dealer, said Thatcher expressed interest in buying military helicopters for a mining enterprise in Sudan. Du Toit described the meeting as a "normal business deal."

Thatcher was scrutinized by Britain's Parliament in 1994 over reports that he was involved in arms sales to Saudi Arabia and Iraq while his mother was prime minister.