Defending her decision to launch air strikes on Bashar al-Assad’s government without consulting parliament, the Prime Minister said chemical attacks on Syrian civilians were a “stain on humanity” and military action was “right thing to do in our national interest”.

Mrs May accused Russia and the Syrian regime of seeking to cover up evidence of the suspected chlorine attack on the rebel-held enclave of Douma, in the suburbs of Damascus.

MPs debated military action in Syria late into the night after the Prime Minister answered questions for over three hours, with further debate today on the role of parliament in approving military action, following an emergency request from Labour leader Jeremy Corbyn.

Protests against the campaign in Syria. (AP Photo/Matt Dunham)

Responding to calls from Labour and the SNP for weapons inspectors to examine the scene of the attack before any further military action, Mrs May said the regime and its backers were blocking a team from the Organisation for the Prohibition of Chemical Weapons (OPCW) that has been in Syria since Friday.

She told MPs: “The Syrian regime has reportedly been attempting to conceal the evidence by searching evacuees from Douma to ensure samples are not being smuggled from this area and a wider operation to conceal the facts of the attack is under way, supported by the Russians.”

The Prime Minister told MPs that waiting for UN authority before considering any military action “would mean a Russian veto on our foreign policy”.

Mrs May added: “We support strongly the work of the OPCW fact-finding mission that is currently in Damascus. But that mission is only able to make an assessment of whether chemical weapons were used.

“Even if the OPCW team is able to visit Douma to gather information to make that assessment – and they are currently being prevented from doing so by the regime and the Russians – it cannot attribute responsibility. This is because Russia vetoed in November 2017 an extension of the joint investigatory mechanism set up to do this.”

Mr Corbyn said the Prime Minister’s humanitarian justification for air strikes was “legally questionable” and faced cries of “shame” as he told Mrs May she was accountable to parliament and not the “whims” of Donald Trump.

The Labour leader questioned whether the regime was responsible for the atrocity on 7 April, saying: “While much suspicion rightly points to the Assad government, chemical weapons have been used by other groups in the conflict.”

Mr Corbyn called for a War Powers Act to put a convention requiring parliamentary approval for military action into law, but critics on his backbenchers were cheered as they praised the Prime Minister for taking military action.

Senior Tory Ken Clarke said he supported the air strikes, but called on Mrs May to establish a cross-party commission to look at parliament’s role in approving military action.

Ian Blackford, the SNP’s leader in Westminster, said it was “perfectly possible” for the House to have been recalled before Saturday’s air strikes. Mr Blackford welcomed Labour support for a War Powers Act “to protect us from getting into this situation again”, and called on the UK government to accept more refugees from the Syrian conflict.

Yesterday Nicola Sturgeon said condemnation of events in Syria cannot “become a blank cheque for western governments to engage in ineffective and potentially counterproductive military action”, and claimed air strikes “felt more like the latest act in a power play between presidents Trump and Putin than any serious attempt to resolve the conflict in Syria”.

The Russian embassy in London accused Mrs May of making “misleading” claims about the OPCW. “It’s Russia and Syria who invited OPCW experts and have been working hard to ensure speedy arrival,” the embassy said on Twitter.

It accused the Prime Minister of basing her attack on Syria on “staged” photos and films.

Russian foreign minister Sergey Lavrov warned relations between Moscow and the west were “worse” than at the time of the Cold War, claiming the UK, Nato and European Union had closed the normal channels of communication that provided safeguards against confrontation.

Theresa May accuses Russia of cover up and denies following Trump's lead