Libya has been warned the UK will not tolerate the "extra-judicial assassination" of Saif al-Islam after reports emerged that he had been captured.
Libyan militia commander Bashir al-Tlayeb told a press conference that the son of former dictator Muammar Gaddafi was captured in Southern Libya with two aides, who were trying to smuggle him out to neighbouring Niger.
He is being taken to the city of Zintan in Northern Libya and is in good health, according to the National Transitional Council's Mohammed al-Allagui.
Former Lib Dem leader Sir Menzies Campbell said Libya must now prove it deserves its place among "civilised nations" by following "due process" in dealing with Saif al-Islam, who is wanted by the International Criminal Court for crimes against humanity.
He said: "The government of Libya is on trial. Anything other than due process should not be tolerated.
"The UK did not commit in Libya to tolerate extra-judicial assassination as happened with his father.
"If Libya wishes to take its place among civilised nations it must take this opportunity to demonstrate it's commitment to the rule of law."