Stop the War Coalition say airstrikes by UK and US will strengthen, not weaken Muammar Gaddafi's position

The Stop the War Coalition has condemned Britain and its allies for launching a "new war" in the Middle East after the "bloody and failing" occupations of Iraq and Afghanistan.

A spokesman for the campaign said: "Air attacks on Libya will not help end the civil war but will escalate it and could be the prelude to a much wider war. They will not help bring the downfall of Gaddafi. He is already portraying the UN's decision as an act of western colonisation and himself as the defender of Libyan sovereignty. Air strikes by the US and Britain will strengthen, not weaken, his position."

"History shows us that the consequences of western intervention are almost always disastrous and not in the interests of those it claims to support."

Andrew Murray, national chair of the coalition, wrote that the decision to "attack Libya and impose regime change" was "instigated by the despots of the Arab League, desperate to secure deeper western involvement in the region to save them from their own peoples".

But the coalition could name just four MPs who were supporting its stance: Labour's Jeremy Corbyn, John McDonnell and Paul Flynn and the Green party's only MP, Caroline Lucas.

In the Commons, Corbyn, MP for Islington North, said: "Is the prime minister now suggesting we should develop a foreign policy that would be prepared to countenance intervention elsewhere where there are attacks on civilians, such as Saudi Arabia, Oman or Bahrain? I hope he has thought this whole thing through."

McDonnell told the Commons: "I support the freedom struggle and I'm a supporter of the United Nations but I have grave and serious concerns about the use of force by western powers in this region, both the short-term and long-term consequences. In the short term, in the interest of conflict resolution, is there to be a final offer from the United Nations to Gaddafi for peace talks?"

Corbyn and McDonnell have rushed out an amendment ahead of a Commons debate on Monday calling on the government to exhaust peaceful attempts at conflict resolution under the auspices of the UN and directly involve other Arab nations before, and during, any deployment of armed force.

Lucas said Britain had "lost the moral authority" when it came to military intervention in the wake of Iraq and Afghanistan. UN resolution or not, she said: "I very much worry that this would be portrayed by Gaddafi as yet more neocolonial exploits."

This evening, Stop the War Coalition said around 80 people took part in a protest outside Downing Street and that further protests were planned.

The Campaign for Nuclear Disarmament said: "CND regrets the British government's decision to pursue military intervention in Libya and urges a political and diplomatic response to the Libyan regime's ceasefire declaration.

" Intervention is difficult and dangerous and runs the risk not only of major civilian casualties but also escalation into a major war in Libya and even further afield.

"The lessons of the last decade's interventionist wars have not been learned: military intervention is not the answer to the just demands of the Libyan people for freedom and democracy. CND urges political solutions including increased sanctions on the Libyan regime and calls on the British government to guarantee that civilian life will be protected and depleted uranium munitions will not be used in any attacks."

• This article was amended on 21 March 2011 to include a link to a letter written by Paul Flynn saying he is not against a no-fly zone in Libya.