Islamic State (IS) terrorists could now be armed with chemical weapons if Britain had not acted to thaw relations with Muammar Gaddafi, Tony Blair has insisted.
The former Prime Minister mounted a robust defence of his diplomatic detente with the Libyan dictator, arguing that otherwise his stockpile of illegal armaments could still be in circulation.
Mr Blair also disclosed that he telephoned Gaddafi "two or three" times in 2011 to try to get him to give up power peacefully - but refused to criticise David Cameron for using force to overthrow the regime.
The comments came as the ex-premier gave evidence to the cross-party Foreign Affairs Committee's investigation into the UK's policy towards Libya.
Mr Blair met Gaddafi in his desert tent in 2004, as the north African country began its return to the international community after years of isolation for supporting terrorism.
As part of the process, Gaddafi renounced weapons of mass destruction, bringing to a halt programmes to develop nuclear and chemical arms.
Mr Blair said he believed his decision to engage with Libya remained "important" in the present day, after IS - also known as Isil, Isis or Daesh - established a presence in the country in the chaotic circumstances which followed Gaddafi's removal and death in the 2011 revolution.
"Otherwise, we would have had a situation where Libya was continuing to sponsor terrorism, was continuing to develop chemical and nuclear weapons and would have remained isolated in the international community," he said.
"I think it is important that we brought them in from the cold, as it were, and important also in today's context because I think - particularly if we had still had the residue of that chemical weapons programme in Libya today, given the state of Libya today and given the presence of Isis there - it would have constituted a real risk, even today."
Mr Blair said the decision to engage with Gaddafi, whom he described as an "unusual" character, had been "difficult because of the nature of the regime and the individual we were dealing with".
"But on the other hand, I think it was worthwhile, because of the protection of our security and because of the broader interest of trying to engage a country like that in a process of change," he added.
He insisted that "evolution is better than revolution".
"Who knows what would have happened if the Arab Spring had not erupted. It may have been a more peaceful evolution," he said.
The former PM confirmed he continued to make visits to Libya after leaving office in 2007, saying he felt it was "important to see if it was possible to get them to do the political and economic reform that followed their switch from the position on security".
Mr Blair said he had "never had any business interests in Libya", but would talk with Gaddafi about the Middle East peace process and Africa as well as the prospects for Libya to open up its economy and make political change.
Mr Blair denied that Libyan involvement in the Lockerbie bombing and the shooting of WPc Yvonne Fletcher had been set aside as part of efforts to bring Gaddafi on side.
"We raised the case of Yvonne Fletcher every time. We did not hold back on Lockerbie and Yvonne Fletcher," he said.
He pointed out that compensation payments for both crimes had been agreed under his Labour government.
The information the UK received from Libya on terrorism was "invaluable for our security services", he argued.
Mr Blair confirmed that he had tried to persuade Gaddafi to give up power peacefully during the Arab Spring revolutions in 2011.
Asked about the military intervention David Cameron undertook against Gaddafi that year, Mr Blair said: "You often find people saying look wouldn't it just be better if we dealt with the dictators? At least when we had Assad there and Saddam there and Gaddafi there, and Ben Ali there we knew what we were dealing with.
"I completely understand that argument, by the way.
"But I think what the Arab Spring shows you is that however much we may want to have dealt with these people, the populations of these countries are not going to tolerate it.
"In particular they are not going to tolerate a tiny group of people often unrepresentative of the majority in the country running the country.
"I can tell you today obviously Libya is a real security problem, it is a security problem for us actually here.
"But I don't think you can make the judgment as to whether it would be better if we had not intervened.
"Because you then have got to say how that would that then have played out as Gaddafi tried to cling on to power and others tried to remove him. You can look at Syria today where we didn't intervene by the way and say that is even worse."
Mr Blair suggested if he had still been in Downing Street he would have tried to use his relationship with Gaddafi to persuade him to go, but he could not know whether it would have worked.
"I am not going to criticise the Prime Minister or (then French president) Nicolas Sarkozy or anyone else," he added. "I know how difficult these decisions are.
"I am sure they did it for reasons that are perfectly well intentioned and in good faith."
Mr Blair denied he had been trying to "save" Gaddafi during two or three telephone conversations in 2011 urging him to agree to a peaceful transition of power.
"They were all to the same effect," the former premier said. "This was all over the space of about 24 hours.
"They were all basically saying there is going to be action unless you come up with an agreed process of change."
Mr Blair said he had spoken to Mr Cameron and US Secretary of State Hillary Clinton informing them that he was going to reach out to Gaddafi as a private citizen.
"They were completely non-committal obviously but listened to what I had to say," he added.
"He (Mr Cameron) was perfectly content, without any commitment at all ... for the conversation to happen."