THERESA May is set to call an emergency meeting of her National Security Council today after her midnight ultimatum for Russia to explain the nerve agent attack in Salisbury expired last night.

It comes as Russia lashed out at Mrs May with sinister nuclear threats yesterday as a stand-off over the outrage escalated.

12 Theresa May's midnight ultimatum to Russia demanding answers to the nerve agent attack has expired Credit: Getty Images - Getty

12 It is almost certain the powerful Novichok nerve agent attack on the Russian spy was a state sponsored assassination bid by Vladimir Putin Credit: EPA

Yesterday a Russian foreign ministry spokesman issued a chilling warning not to “threaten a nuclear power”.

But Britain received support from the US, Germany, France and other EU leaders.

President Trump told Mrs May: We are with you all the way.”

Tensions rocketed after the Russian Embassy in London formally refused Mrs May’s demand to come clean over the attack with a series of tweets posted from 5.30pm.

What we know so far:

The embassy insisted: “Moscow will not respond to London’s ultimatum until it receives samples of the chemical substance to which the UK investigators are referring”.

Adding another dark warning, it added: “Any threat to take ‘punitive’ measures against Russia will meet with a response. The British side should be aware of that”.

She will now return to the Commons to declare the poisoning of Sergei Skripal and daughter Yulia a state—sponsored assassination bid — almost certainly ordered by President Vladimir Putin.

12 US President Trump told Theresa May 'We are with you all the way' Credit: AFP or licensors

12 Theresa May said today that Russia was behind the poisoning attack on Sergei Skripal Credit: PA:Press Association

12 Russian Foreign Ministry spokeswoman Maria Zakharova issued a chilling warning to the PM warning her not to 'threaten a nuclear power' Credit: Reuters

12 Russian Foreign Minister Sergei Lavrov gestures during a meeting Credit: EPA

1/7 UK Ambassador Laurence Bristow was summoned to @MFA_Russia, where First Deputy FM Vladimir Titov strongly protested the evidence-free accusations by the UK authorities of Russia’s alleged involvement in the poisoning of Sergei Skripal and his daughter Yulia. pic.twitter.com/wQvl2AwLJI — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

2/7 It was stated that the actions of the UK authorities are a clear provocation and that the Russian Federation was not involved in the incident that took place in Salisbury on 4 March, 2018. pic.twitter.com/WppmgfgO6L — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

3/7 Moscow will not respond to London’s ultimatum until it receives samples of the chemical substance to which the UK investigators are referring. pic.twitter.com/B5CNtimcc3 — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

4/7 Britain must comply with the Chemical Weapons Convention which stipulates joint investigation into the incident, for which Moscow is ready. pic.twitter.com/8TxEBOpBQ8 — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

The PM will unleash what is expected to be a tough package of “extensive measures” to punish the Kremlin for the attack, including expulsions, economic sanctions, travel bans and asset freezes.

Downing Street was delighted by the support offered to Mrs May by Western leaders on Tuesday night.

Mrs May spoke to President Trump who was on board Air Force One. He told travelling reporters: “It sounds to me like they believe it was Russia and I would certainly take that finding as fact”.

The White House added: “The two leaders agreed on the need for consequences for those who use these heinous weapons in flagrant violation of international norms.”

The PM received pledges of solidarity in conversations with French president Emmanuel Macron, Germany’s Angela Merkel, and the EU.

5/7 Without that, there can be no sense in any statements from London. The incident appears to be yet another crooked attempt by the UK authorities to discredit Russia. pic.twitter.com/VLk6UCePVj — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

6/7 Any threat to take “punitive” measures against Russia will meet with a response. The British side should be aware of that. pic.twitter.com/DFAaB5orQE — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

7/7 Today the Embassy sent a note to @ForeignOffice reiterating that Russia is not involved in the Salisbury incident and outlining the above mentioned demands for joint investigation pic.twitter.com/Vj5mxFBpfA — Russian Embassy, UK (@RussianEmbassy) March 13, 2018

12 Russian spy Sergei Skripal and his daughter Yulia are fighting for their lives in hospital following nerve agent attack in Salisbury

12 Army chemical weapons experts and the police swarmed on sleepy Winterslow Credit: PA:Press Association

12 Vladimir Putin was pictured smirking when BBC reporter Steve Rosenberg directly asked him if Russia was behind the poisoning of Sergei Skripal Credit: BBC

But insisting the Kremlin is “not to blame”, Russian Foreign Minister Sergei Lavrov said London would be “better off” complying with its international obligations “before putting forward ultimatums”.

Russia summoned Britain’s ambassador to Moscow to relay the same message.

No10 hit back at Lavrov, insisting Mrs May was under no legal obligation to hand evidence to Russia.

Daughter may have 'brought in' chemical By Mike Sullivan, Crime Editor THE daughter of Russian spy Sergei Skripal may have unwittingly brought the deadly nerve agent with her from Moscow. Scotland Yard and MI5 are trying to establish if Yulia Skripal, 33, was being tailed by a Russian agent — or if her luggage or possessions were interfered with en route to the UK. They want to know how Russian military nerve agent Novichok was administered to turncoat Sergei, 66, and Yulia. Yulia arrived on a flight from Russia the day before she and Sergei were found unconscious on a bench in Salisbury, Wilts. Met Police Assistant Commissioner Neil Basu, the UK’s leading counter-terrorism cop, said at the moment they were “not declaring a person of interest or a suspect”. It lends weight to the theory that Yulia may have carried the deadly nerve agent into the UK without her knowledge — or was shadowed by an assassin. As officers continued their work, Mr Basu warned of further disruption to the city — but urged people to stay calm

Foreign Secretary Boris Johnson called the attack on the Skripals “the first use of nerve agent on the European continent since the Second World War”.

He said: “I’ve been very encouraged so far by the strength of the support that we are getting”.

The Foreign Office later said Mr Johnson had called Nato Secretary General Jens Stoltenberg and counterparts in France and Germany to “set out what we know” and the need for an international response.

Politicians heaped pressure on the Football Association to boycott this summer’s World Cup in Russia.

Senior Labour MP John Woodcock said England’s participation “ought to be in question”.

12 Mrs May said the 'Kremlin is intent on dismantling the rules based world order' Credit: AFP or licensors

12 But Mr Lavrov says his country has no connection to the incident Credit: Getty

12

Lib Dem boss Sir Vince Cable urged Mrs May to pursue an EU-wide boycott of the tournament.

He said the World Cup would be “pointless” if all ten European nations pulled out.

He added: “Do it collectively. That would really hurt them.”

Boris Johnson refused to rule out a boycott — although any decision would be taken by the FA and not the Government.

Mrs May has tasked spy chiefs to devise covert operations to embarrass President Putin and his oligarch cronies in revenge for the Salisbury attack.

Ministers want the deniable operations mounted against senior Kremlin figures, which are likely to include exposing their vast treasure troves of hidden wealth.

A senior security source said: “We’re going to play Putin at his own game. The gloves are off now”.

5 WAYS TO HIT BACK 1 — Kick out Russian diplomats: David Cameron did this after Alexander Litvinenko was poisoned in 2006. But the Kremlin would ­probably retaliate.

2 — Strip Russian media of its right to broadcast in the UK: PM could ask Ofcom to declare channels such as RT — formerly Russia Today — not fit to hold a licence.

3 — Stay away from World Cup in Russia: EU sport officials could be urged to boycott event, but this would not involve footballers.

4 — Toughen up sanctions: The Government could amend the ­sanctions and anti-money laundering bill to impose firmer rulings against human rights abusers.

5 — Freeze assets of Russian oligarchs: But this might hit as many Putin opponents as allies.

PM Theresa May confirms that Russia is 'highly likely' to have carried out the attack on former spy Sergei Skripal in Salisbury using military-grade nerve agent

What is Novichok and was the nerve agent used to poison ex-Russian spy Sergei Skripal? Novichok - the Russian for newcomer or newbie - is the name for a series of nerve agents developed by the Soviet Union in the 1970s and 80s. They are said to be the deadliest nerve agents ever created and reported to be five times more potent than the notorious VX gas. It is made of two relatively harmless materials which become fatal when mixed together, making it easier to transport under the radar. "It is designed to be undetectable for any standard chemical security testing, " Colonel Hamish de Bretton-Gordon told the Express. Novichok agents, dispersed as an ultra-fine powder rather than vapour, belong to the class of inhibitors called "organophosphate acetylcholinesterase". They prevent the normal breakdown of a neurotransmitter acetylcholine which, when it builds up, causes muscles to contract involuntarily. Because the victim's heart and diaphragm aren't functioning properly, this leads to respiratory and cardiac arrest. Those affected usually die from total heart failure or suffocation as copious fluid secretions fill their lungs. But even if they don't die from the nerve agent, the substance can also cause permanent nerve damage, leaving victims permanently disabled, Russian scientists have said.

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Eavesdropping experts GCHQ have top hackers and can penetrate well hidden money trails.

Some estimates make President Putin the richest man in the world, with an £80billion fortune.

Exposing his riches would deeply embarrass him in front of electors as he goes to the polls.