David Cameron approved the decision to allow Moussa Koussa, the Libyan foreign minister, to defect to Britain with at least one member of his family after consulting the US, Downing Street said today.
As William Hague made clear that no deal had been struck to offer him immunity from British or international justice, senior figures indicated that Koussa has been Britain's main conduit to Muammar Gaddafi's regime for at least a decade.
Hague said this morning that Koussa, who is under armed guard at a safe house with his son, has been "my channel of communication to the regime" in recent weeks, even after the launch of coalition air strikes.
In signs of Britain's close links with Koussa:
• Jack Straw, the former foreign secretary, described him as a "key contact" for Britain, who played a "fundamentally important role" in persuading Gaddafi to give up his nuclear and chemical weapons programme in 2003. Koussa held negotiations with MI6 officers at the time.
• Oliver Miles, Britain's former ambassador to Tripoli, said that Koussa's main contacts with Britain date back to Gaddafi's decision under the last Conservative government to abandon Libya's support for the IRA.
Hague, who was speaking at the launch of the foreign office's 2010 Human Rights and Democracy Report, gave further details about the defection of Koussa, who fled to the UK on Wednesday in a specially arranged flight from Tunisia organised by the British intelligence services. Koussa said he was "no longer willing" to represent Gaddafi's regime.
"I can confirm … that the Libyan foreign minister, Moussa Koussa, arrived at Farnborough Airport yesterday from Tunisia. He travelled here under his own free will; he said that he is resigning his post. We're discussing this with him and we will release further details."
The foreign secretary seized on Koussa's defection to claim that Gaddafi's regime was crumbling. "Moussa Koussa is one of the most senior members of the Gaddafi regime, he has been my channel of communication to the regime in recent weeks and I've spoken to him several times on the telephone, most recently last Friday.
"His resignation shows that Gaddafi's regime, which has already seen significant defections to the opposition, is fragmented, under pressure and crumbling from within. Gaddafi must be asking himself who will be the next to abandon him. We reiterate our call for Gaddafi to go."
Hague confirmed that his former Libyan counterpart had not been offered immunity from prosecution. "Moussa Koussa is not being offered any immunity from British or international justice. He is voluntarily talking to British officials at the moment, including members of British Embassy in Tripoli – which is, of course, now based in London – and our ambassador, Richard Northern."
Downing Street said that Cameron had approved the decision to allow Koussa to defect to Britain after consulting the US authorities. "There was some contact with the US," the prime minister's spokesman said.
Asked whether the prime minister had approved the decision to allow Koussa to land in Britain, he said: "We clearly had a judgment we had to make about his entry."
The prime minister's spokesman added: "He arrived on a private plane from Tunisia. He made his own way to Tunisia. We did have some knowledge of his intention to come to the UK, so he was met by British officials on arrival in the UK.
"He is currently at a safe location in the UK and he is meeting with British officials, in particular those officials from what was our embassy in Tripoli."
Koussa's defection has led to expectations that he will be questioned about his possible involvement in or knowledge of atrocities including the Lockerbie bombing and the murder of PC Yvonne Fletcher. Koussa was expelled from the UK in 1980 and was head of Libyan foreign intelligence for 15 years, including the period of the Lockerbie bombing in 1988. He has always denied Libya was involved in the bombing.
The prime minister's spokesman said it was up to the Scottish and English legal authorities if they wanted to question Moussa on the Lockerbie bombing or the murder of Fletcher.
"The position on Lockerbie is that there is an investigation, led by the Scottish authorities, that is still open. That is a matter for the Scottish authorities, not Her Majesty's Government. I'm not clear that any request has been made.
"The same applies on [Fletcher]. There is an investigation that is still open. That would be a matter for the police."
Straw shed light on Britain's close contacts with Koussa when he described him as "the key figure" in the negotiations that led to Gaddafi abandoning his WMD programme in December 2003.
The former foreign secretary told the Today programme: "Moussa Koussa was fundamentally important in those negotiations. He was one of the key figures, if not the key figure, in the Libyan regime who was negotiating with British officials secretly – and then after 19 December 2003 [when] it was known the negotiations were taking place.
"This was an existential negotiation for Libya because Gaddafi had been building up very covertly a very substantial nuclear weapons capability and a chemical weapons capability.
"I am in absolutely no doubt that he played a fundamentally important role in getting Gaddafi to agree to give up his nuclear weapons programme and his chemical weapons programme."
Straw confirmed that Koussa's contacts with Britain date back more than a decade, adding: "He has been an absolutely fundamentally important person in the operation of the Libyan regime, which itself is a shadowy regime."
Oliver Miles, Britain's former ambassador to Libya, said that Koussa was involved in the negotiations to bring "Libya in from the cold" under the last Conservative government.
Miles told Today: "By the time he emerged as first deputy foreign minister and then as head of external intelligence, he came to those important positions at the time when we were bringing Libya in from the cold.
"The very first part of bringing Libya in from the cold … under the [previous] Conservative government was when Libya satisfied the British government that they were no longer supporting the IRA."
Miles said that Britain had been familiar with the "negative side" of Koussa. "I was involved in some of the negative side when we threw him out of London in 1980 when he had endorsed the policy of killing what Gaddafi called 'stray dogs', meaning opposition Libyans. Two of them had been killed in London."