The British-educated son of Libya's leader says the country's foreign minister defected for health reasons and has no new information to offer UK authorities questioning him about the Lockerbie bombing.
British officials are encouraging Musa Kusa, who resigned from Muammar Gaddafi's government and fled to the UK last week, to answer questions from Scottish prosecutors about the terrorist atrocity.
Gaddafi's son, Seif al-Islam, repeatedly called Musa Kusa "sick and old" in an interview with the BBC, suggesting Kusa might resort to making up "funny stories" about Lockerbie and Gaddafi in exchange for immunity.
He says British and US officials "know everything about Lockerbie so there are no secrets" Kusa can reveal.
UK police and prosecutors said steps are being taken to arrange the appointment "in the next few days".
Scottish investigators are expected to question him over the bombing after discussions with Foreign Office officials on Monday.
Kusa was head of Gaddafi's feared intelligence agency from 1994 and was a senior intelligence agent when PanAm flight 103 was blown up over Lockerbie, killing 243 passengers, 16 crew and 11 residents.
Libyan Abdelbaset al-Megrahi was jailed for mass murder in 2001 but was returned to Tripoli in 2009 on compassionate grounds after doctors treating him for prostate cancer gave him an estimated three months to live.
As well as the Lockerbie bombing, shadow home secretary Yvette Cooper has led calls for Kusa to be quizzed in relation to the murder of Pc Yvonne Fletcher, who was shot during a protest outside London's Libyan Embassy in 1984.