Foreign policy heavyweights in the Commons have lent cautious support to military action in Libya, while expressing unease at the long term plan.
In a vote later this evening MPs are expected to overwhelmingly back David Cameron's decision to commit British armed forces to the United Nations backed mission.
Former Labour defence secretary Bob Ainsworth said he was a late convert to the case for taking military action against Colonel Gaddafi.
"It is relatively easy to support things on day one, it is relatively difficult to support them on month three or month nine," he said.
Ainsworth, who oversaw the conduct of the war in Afghanistan under Gordon Brown, said he was "unashamedly reluctant and late" in his support.
"I would not be giving my support for this resolution tonight if it were not for the fact the UN has given its support."
And he warned the Commons that he was "somewhat concerned by the degree of enthusiasm" among some sections of the media, the public, and the Commons for getting involved in "yet another operation abroad".
Former Liberal Democrat leader and foreign affairs committee member Menzies Campbell said the action taken in Libya was different from the 2003 invasion of Iraq as it had the support of the UN.
"I voted against military action against Saddam Hussain," he said. "If I thought the present action was illegitimate I should have no hesitation in voting against it."
"If you ask your young men and women to put their lives at risk as we do then the cause must be just not just in strict legal terms but in political and even social terms as well."
Campbell, who is a member of the Commons foreign affairs committee, said action was "necessary, legal and legitimate".
"The lives of his people have been threatened in recent times by a immediate and chilling promise to go from house to house, from room to room, and to show no mercy.
"I invite the House to consider this; supposing we had allowed a slaughterhouse to take place in Benghazi what would have been the nature and terms of the debate today?
"I believe it to be legal because of the express authority of a Security Council resolution.
"This action springs from a universal repugnance of the international community against the brutal excesses of the Gaddafi regime and has regional support of the Arab League and the Gulf Cooperation Council.
"Gaddafi will be a dangerous opponent. Deceit, deception and defiance have kept him in power for many, many years.
"To maintain an international coalition will require both skill and sensitivity."
Jack Straw said UN resolution 1973 was a "of historic significance" to which he gave his "wholehearted support".
Straw, who was foreign secretary under Tony Blair at the time of the 2003 invasion of Iraq, praised David Cameron and William Hague for their "indefatigable work" in taking action against Gaddafi.
"Two weeks ago I re-watched hotel Rwanda, a chilling film portrayal of the massacres of defenceless civilians hacked to pieces by the so-called forces of law and order," Straw told the House.
"In July 2005, when the UK had the EU presidency, I went to Srebrenica for the tenth commemoration for day in 1995 when 10,000 unarmed civilians were brutally murdered by the forces of law and order.
"In Rwanda and in Bosnia the UN had solemnly considered what it should do.
"In both theatres there were already blue-hatted UN troops on the ground but who then stood by as massacres took place in front of them.
"Those UN troops were there as peacekeepers however there was no peace to keep."
Straw said: "Doing nothing in the face of evil is as much a decision with consequences as doing something about that evil."
He said the result of doing nothing would have been "industrial scale slaughter".
Defence committee chair James Arbuthnot said he was proud of Cameron and Hague for displaying "not only real clarity about what is right and wrong but a willingness to risk rebuff and potential humiliation".
But he said "serious questions need answering" about the commitment of British forces.
"What do we want to achieve?" he asked "With what will we be satisfied?"
And he said: "What is our strategy in reaching whatever end state we will be satisfied with?"
Conservative Rory Stewart said the wider regional impact of the action in Libya had to be considered.
"This is not something that began in Libya it's not something that is going to end in Libya," he said.
"This is a response primarily to Egypt and Tunisia.
"If we had stood back at this moment and done nothing, if we had allowed Gaddafi it simply hammer Benghazi, people in Egypt and Tunisia and Syria, people would have conclude we were on the side of oil rich regimes against their people."
Stewart, who is a member of the foreign affairs committee and a former FCO official, said this would have left the West with "no progressive narrative" with which to deal with the region.
But he warned, as many other backbenchers had, that "if you dip your toes in you are very soon up to your neck".
He added: The most important thing for us now is to be careful with our language and careful with our rhetrotic."


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