Mark Thatcher has been released on bail by a South African court following his arrest in connection with an alleged coup attempt in Equatorial Guinea.
Sir Mark was arrested at his home
The son of former UK Prime Minister Margaret Thatcher was ordered to pay a bail bond of two million Rand (£165,000) and hand over his passport.
He was charged with contravening two sections of South Africa's Foreign Military Assistance Act.
The act bans residents from taking part in any foreign military activity.
Sir Mark, who inherited his late father's hereditary baronetcy in 2003, appeared in court in a dark suit and said nothing during the short hearing.
He has been bailed to return to the court on 25 November and has been ordered not to leave the district and to hand over his passport and travel documents to the South African authorities.
The 51-year-old father-of-two was arrested at his home in an exclusive suburb of Cape Town.
A spokesman for South Africa's National Prosecuting Authority said he had been arrested on suspicion of providing funding and logistical assistance.
Speaking outside the court, Sir Mark's lawyer, Peter Hodes, said he had been held on suspicion of providing financing for a helicopter linked to the coup plot and intended to plead not guilty.
After the hearing, a spokesman for Sir Mark said he was "innocent of all charges" made against him.
A spokeswoman for Baroness Thatcher said the former prime minister was on holiday in the United States and had not yet been contacted.
Sir Mark's twin sister, Carol Thatcher, told BBC News 24 she was shocked by the allegations against her brother but that she had "lived through scandals before".
Speaking at Heathrow Airport, as she returned to London from Switzerland, she said she had not spoken to Sir Mark and did not know the details of the charges against him.
She said: "My real concern is for my mother because she's in America and I haven't spoken to her and I don't know her reaction and I care about her."
She said she planned to contact Baroness Thatcher straight away before trying to get hold of her brother.
An alleged plot to overthrow the president of Equatorial Guinea has sparked dozens of arrests across Africa.
South African arms dealer Nick du Toit is accused of helping to organise the coup.
He went on trial with 13 other foreign nationals on Monday in the country's capital, Malabo.
The eight South Africans and six Armenians have been detained since March this year.
A 15th defendant died in prison. Both Amnesty International and Mr du Toit's wife allege the accused were tortured.
Seventy other accused mercenaries are on trial separately in Zimbabwe, where
they were arrested on 6 March as they allegedly prepared to board a leased
aircraft to launch the coup.
The alleged plot leader, former British SAS captain Simon Mann, an old Etonian turned leading African mercenary, has admitted trying to procure dangerous weapons - a charge which carries a possible 10-year jail sentence.