THERESA May has given Vladimir Putin until the end of today to come up with a credible response to the claim Russia was behind the chemical weapon attack in Salisbury or face a “full range of measures” from the UK.

In an emergency Commons statement, which followed a meeting of the National Security Council, during which the Prime Minister received the latest intelligence analysis, she said it was now “highly likely” Moscow was behind the “brazen, indiscriminate and reckless” attack on the former Russian spy Sergei Skripal, 66, and his daughter Yulia, 33.

The attempted murder amounted to an “unlawful use of force against the UK,” insisted Mrs May.

READ MORE: Russia dismisses Theresa May's ultimatum over chemical attack as "circus show"

The PM explained the substance used was a "military-grade" nerve agent produced by Russia and there were only two possible explanations: either Moscow was behind the attack or it had lost control of its stockpile of the poison.

She revealed the UK Government had summoned the Russian ambassador to the Foreign Office and given him until the end of Tuesday to “immediately provide full and complete disclosure” of his country’s Novichok nerve gas programme to the Organisation for the Prohibition of Chemical Weapons.

However, the initial response from the Putin Government was dismissive. A Kremlin spokesman said Mrs May's statement to MPs was a “circus show” and that Britain was peddling “fairy tales”.

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In a sombre atmosphere, the PM told MPs: "This attempted murder using a weapons-grade nerve agent in a British town was not just a crime against the Skripals, it was an indiscriminate and reckless act against the United Kingdom, putting the lives of innocent civilians at risk.

"And we will not tolerate such a brazen attempt to murder innocent civilians on our soil," she declared.

Mrs May explained how she would return to the Commons on Wednesday following the Tuesday midnight deadline to give her Government’s reaction to what Russia had said.

"Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian State against the United Kingdom."

This, she stressed, would result in her setting out "the full range of measures that we will take in response".

READ MORE: Nerve agent in Salisbury attack ‘clearly came from Russia’, says Rex Tillerson

This could include expelling a raft of diplomats, exacting new sanctions against Russian officials involved in corruption and human rights abuse along the lines of the US Magnitsky Act and even seizing the UK property of the Russian President’s allies in the UK.

Conservative MP Tom Tugendhat, who chairs the Commons Foreign Affairs Committee, said: “This is not an act of war but it’s certainly a war-like act by the Russian Federation.”

The Kent MP urged Mrs May to call on allies like the EU, the US and Nato and “ask what they will do to assist us in this moment when we are in need”.

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No 10 later suggested there had already been international contacts from senior UK officials and that the PM would be talking to her foreign counterparts in the coming hours.

In the chamber, Jeremy Corbyn was heckled when he called for Britain to continue to seek a “robust dialogue with Russia on all the issues dividing our countries, both domestic and international,” rather than simply cutting off contact and simply letting tensions and divisions get worse, and potentially even more dangerous.

The Labour leader faced shouts of "shame" and "disgrace" from Conservative MPs as he told the Commons: "We're all familiar with the way huge fortunes, often acquired in the most dubious circumstances in Russia, sometimes connected with criminal elements, have ended up sheltering in London and trying to buy political influence in British party politics.

"Meddling in elections, as the Prime Minister put it, and there has been over £800,000 worth of donations to the Conservative Party from Russian oligarchs and their associates."

Ian Blackford for the SNP denounced the Salisbury incident as an “international outrage” and said it was important everyone worked together to get to the bottom of it.

“There can be no denying that this assassination attempt on Sergei Skripal and his daughter Yulia is not only a step too far by those responsible but it calls into question every aspect of our current and future relationship with Russia,” declared the Nationalist leader.

He said the “ruthless” chemical attack had not only endangered the lives of emergency services but also threatened the health of the public enjoying a Sunday afternoon.

“Everyone has the right to live in the UK in security and safety and any challenge to those rights needs to be responded to in an appropriate manner,” he added.

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Vince Cable for the Liberal Democrats suggested one of the most effective ways of “punishing Russia for these appalling activities” would be to seize the private property assets in Britain of the Putin Government and its associates.

Iain Duncan Smith, the former Conservative leader, berated Mr Corbyn for failing to "abandon party politics" on such a serious matter as he said, after Crimea, Ukraine and Syria, Russia was now as close to being a “rogue state” as it could be.

Labour's Mike Gapes called on the PM to talk with Tony Blair over Russia's response to British actions after the 2006 murder of Alexander Litvinenko, which was laid at Russia's door.

"It's quite clear the Russians will retaliate and we will then be into a tit-for-tat process," noted Mr Gapes. "They think we will back down. We've got to say, resolutely and strongly, we are not backing down. This is an act of terrorism and all Members of Parliament should stand together," insisted the London MP.

READ MORE: Russia dismisses Theresa May's ultimatum over chemical attack as "circus show"

Earlier, the Russian President dismissed questions about his state's alleged involvement in the Skripal case.

On a visit to a grain centre, he told the BBC: "We're dealing with agriculture here...and you talk to me about some tragedies. Get to the bottom of things there, then we'll discuss this."