BRITAIN has a responsibility to take action to punish the "morally indefensible" use of chemical weapons by the Syrian regime even without a UN mandate, David Cameron has suggested.
In his first public comments on the crisis, the Prime Minister said today that the Government was considering "legal and proportionate" means to "deter and degrade" Assad's chemical weapons capability.
Syria crisis: UK and US vow that any military response is 'not about regime change' as Parliament is recalled
But Mr Cameron and his deputy, Nick Clegg, appeared to imply that such action could take place without a mandate from the UN Security Council - or without waiting for weapons inspectors to report on their examination of the site of the alleged attack in Damscus last week, during which hundreds are reported to have died. Foreign Office lawyers and the Attorney General, Dominic Grieve, are understood already to have examined the legal route for military intervention in Syria using a controversial UN " humanitarian" exemption that allows action without the Security Council's authority.
Western intervention in Syria is likely to take the form of limited cruise missile strikes against regime targets and sites identified with chemical weapons sites. It is expected to take place within the next 10 days.
In echoes of Tony Blair's argument that there was a "moral case" for the war in Iraq even without a UN mandate, Mr Cameron said the use of chemical weapons was "morally indefensible" and Britain could not "let that stand". But unlike Mr Blair he insisted Western action was "not about getting involved in a Middle Eastern war".
"I understand people's concerns about war in the Middle East, about getting sucked into the situation in Syria," he said. "This is not about wars in the Middle East, this is not even about Syria. It's about the use of chemical weapons and making sure as a world we deter their use and deter the appalling scenes we have all seen on our TV screens."
"It must be right to have some rules in our world and try to enforce those rules," Mr Cameron added. "Any action we take or others take would have to be legal, would have to be proportionate, it would have to be specific to deter and degrade the future use of chemical weapons."
The Prime Minister said there was never 100 per cent certainty or a single piece of irrefutable evidence of their use, but said the world had agreed almost a century ago they should not be used.
But his stance was attacked by the former Chief UN Weapons Inspector at the time of the Iraq War. Hans Blix said Mr Cameron " doesn't seem to care much about international legality".
"As far as they are all concerned, a criminal act has been committed so now they must engage in what they call retaliation," he said.
"I don't see what they are retaliating about. The weapons weren't used against them. If the aim is to stop the breach of international law and to keep the lid on others with chemical weapons, military action without first waiting for the UN inspector report is not the way to go about it."
Although action based on self-defence has been dismissed as inappropriate by London and Washington, senior Foreign Office lawyers and Mr Grieve believe humanitarian intervention, based on " overwhelming humanitarian necessity", was correctly applied by Tony Blair when he authorised force in Kosovo in 1999, and can be used again.
Mr Cameron initially focused on the "humanitarian" exemption to plan action in Libya, but eventual UN backing rendered it unnecessary.
Following the Kosovo action, the Foreign Affairs Select Committee criticised the "humanitarian" justification as being " illegal" but nevertheless backed its use as "legitimate".
Russia has dismissed the use of the humanitarian route as illegal. The country's deputy Prime Minister, Dmitry Rogozin, went further by accusing the West of behaving like a "monkey with a grenade" over Syria.
Mr Cameron also announced that MPs would be given a vote on a motion during an emergency sitting of the House of Commons on Thursday to discuss Syria.
After speaking to Mr Cameron, Labour leader Ed Miliband said he would consider giving Labour backing to action but only on the basis it could proved to be legal.
"The use of chemical weapons on innocent civilians is abhorrent and cannot be ignored," he said. "When I saw the Prime Minister this afternoon I said to him the Labour Party would consider supporting international action but only on the basis that it was legal, that it was specifically limited to deterring the future use of chemical weapons and that any action contemplated had clear and achievable military goals. We will be scrutinising any action contemplated on that basis."
The Deputy Prime Minister Nick Clegg added that he agreed with Mr Cameron on the need for action.
"If we stand idly by we set a very dangerous precedent indeed, where brutal dictators and brutal rulers will feel they can get away with using chemical weapons on a larger and larger scale in the future," he said.
"So what we're considering is a serious response to that. What we are not considering is regime change, trying to topple the Assad regime, trying to settle the civil war in Syria one way or another. That needs to be settled through a political process."
But the Prime Minister is likely to face significant opposition to any intervention and is likely to face intense questioning over how he can justify the legality of any action without a UN mandate.
Richard Ottaway, chairman of the Commons Foreign Affairs Committee, said international law had changed since intervention in Kosovo, when intervention was justified on the basis overwhelming humanitarian need.
"That doctrine [now] only supports intervention with the backing of a UN resolution, so if China and Russia veto any resolution, then clearly an intervention would not have the legal authority," he told the BBC.
He added: "Unlawful is probably a slightly exaggerated phrase. I think there is no legal support for an intervention of this nature rather than describing it as illegal."
Andrew Bridgen, who sent a letter signed by 81 fellow Conservatives to Mr Cameron demanding a vote earlier this year, said: "The House is going to seek assurance on the grounds for action, that there is compelling evidence it is the Assad regime that launched the chemical attacks - that will need to be proved and explained.
"We will need the aims of any action and limits and scope of action, and information on who else will be involved."