Proceedings against Sir Mark Thatcher over allegations he helped finance a coup plot in Equatorial Guinea have been postponed until 8 April.
Sir Mark was 'furious' at being barred from leaving South Africa.
The son of former Prime Minister Margaret Thatcher had been expected to enter a plea in a South African court, but prosecutors wanted more time.
On Wednesday, the High Court there ruled he must also face questions from Equatorial Guinea investigators.
Sir Mark, 51, says he was feeling like "a corpse" while proceedings go on.
The businessman - who appeared in court for the two-minute hearing - had his bail conditions extended, meaning he is confined to the Cape Town area for at least the next five months
Sir Mark, the son of former Prime Minister Margaret Thatcher, has denied being involved in a plan to topple the government of Equatorial Guinea but is barred from leaving South Africa while investigations continue.
Sir Mark denies the charges.
He was arrested in August at his home in South Africa and released after a bail payment of £167,000 ($314,000) was made.
The businessman had sought to avoid questioning by investigators from Equatorial Guinea, saying the questions would infringe on his right to silence and would impact on his trial in South Africa as well as Equatorial Guinea should he later be extradited.
On Wednesday, Judge Deon van Zyl rejected this argument, saying South African Justice Minister Brigitte Mabandla was within her rights to seek Sir Mark's responses to the Equatorial Guinea questions.
"She was perfectly entitled to accept the existing scenario as an issue of foreign policy and co-operative relations between South Africa and Equatorial Guinea," Judge van Zyl said, adding that Sir Mark's rights would not be compromised.
"At no stage have such rights been violated or even
threatened," he said.
Sir Mark's legal team are still deciding whether to appeal against the ruling.
Equatorial Guinea, Africa's third biggest oil producer, says it intends to extradite him to face similar charges as 14 other suspected foreign mercenaries currently on trial there.
In an interview with Vanity Fair magazine, Sir Mark said he felt like "a corpse" and that he was glad his father was not alive to see his arrest.
Sir Mark told the magazine: "I will never be able to do business again. Who will deal with me?"
He said there were 18,500 references to the case on the day he was arrested in August this year.
"Thank God my father is not alive to see this," he said in the January edition of the magazine, on sale from 3 December.
He was "furious" that he was confined to South Africa, and that his telephone calls and emails are monitored by the authorities there.