Sir Mark Thatcher faces questioning in open court over his role in an alleged coup plot after South Africa approved a request by Equatorial Guinea to interview him.
Yesterday's decision followed a meeting between the Justice Minister, Brigitte Mabandla, and a visiting team of investigators from the oil-rich west African state, headed by the country's top prosecutor. A spokesman said questions would be submitted to a magistrate in Cape Town who would then subpoena Sir Mark.
Under the deal, the Equatorial Guineans would be permitted to listen to his answers, probably in open court. Prosecutors said they expected it to take place "very soon".
Sir Mark, 51, is charged with contravening South Africa's Foreign Military Assistance Act designed to stop the country being used as a base for plotting the overthrow of governments. He has been ordered to remain in the Cape Town area pending a court appearance in November.
South Africa has insisted it will not allow Sir Mark to be extradited to Equatorial Guinea unless it is guaranteed that he will not face the death penalty.
Lawyers in Guernsey acting for Equatorial Guinea's President, Teodoro Obiang Nguema, are seeking to discover the identities of those who allegedly bankrolled the coup attempt, and will seek details of payments made into the account of Simon Mann, who is said to have masterminded the plot. Among those said to have paid in to it is a certain J H Archer - prompting speculation it is Lord Archer, a claim he denies.