David Cameron tonight urged Muammar Gaddafi's "henchmen" to follow the example of his former foreign minister and defect.
The Prime Minister said the fact that Musa Kusa had abandoned the dictator and fled to Britain showed the Libyan regime was "crumbling".
Speaking at a press conference in Downing Street, Mr Cameron said others should now "come to their senses" and change sides.
"The decision by the former Libyan foreign minister to come to London to resign his position is a decision by someone right at the very top," Mr Cameron said.
"It tells a compelling story of the desperation and the fear right at the very top of the crumbling and rotten Gaddafi regime."
Asked what assurances had been given to Mr Kusa and whether he would be handed over to Scottish authorities over the Lockerbie bombing, Mr Cameron said: "Let me be clear, Musa Kusa is not being granted immunity, there is no deal of that kind, of the sort that you ask.
"And the point I would make about the dreadful events over Lockerbie, that investigation is still open and the police and the prosecuting authorities are entirely independent of Government and they should follow their evidence wherever it leads and the Government will assist them in any way possible.
"They are in no way restricted from following their evidence and that is exactly what they should do and we will respond to any requests that they make."
Scottish prosecutors have told the Foreign Office they want to interview Mr Kusa in connection with the 1988 bombing of Pan Am 103 over Lockerbie.
The Prime Minister stressed that Mr Kusa's defection had been a "serious blow to Gaddafi's authority - we shouldn't underestimate that".Reuse content