THERESA May is preparing to name Russia as responsible for the chemical weapons outrage in Salisbury after confirmation from spy chiefs.

The PM’s explosive move will plunge relations between London and Moscow into their worst crisis since the end of the Cold War.

3 PM Theresa May is to summon an emergency meeting of her National Security Council to decide on the scale of Britain’s retaliation Credit: Getty - Pool

A key intelligence assessment of who was behind the nerve agent poisoning is being delivered to No10 overnight, to be on PM’s desk this morning.

In their report to Mrs May, The Sun has learned that MI5 and MI6 chiefs will cite the very rare substance used on ex-spy Sergei Skripal and daughter Yulia as key evidence of the Kremlin’s involvement.

It is believed to have been developed in the SVR Russian foreign spy service’s notorious Yasenevo laboratory.

Mrs May will then summon an emergency meeting of her National Security Council at 11am to decide on the scale of Britain’s retaliation.

3 Commons Foreign Affairs Committee chairman Tom Tugendhat described Russia as a great country that has been taken over by KGB thugs Credit: PA:Press Association

A statement by her to the House of Commons to make the formal charge against Moscow could come as early as this afternoon.

Mrs May could even go so far as heap blame on Vladimir Putin personally.

Under Russian law, foreign assassinations – known as ‘wet jobs’ – must be authorised by Russia’s president.

But ministers are still undecided on exactly when to mount the UK’s retaliation.

A “full spectrum” package of expulsions and economic sanctions has been drawn up, along with a plea for international support for them.

3 Ex-Ambassador to Russia Sir Tony Brenton said the more Putin can point to Western hostility, the more he rallies the Russian people around him Credit: Reuters

But it is feared that a strong reaction ahead of Russia’s presidential elections next Sunday may play into Putin’s hands.

It is suspected that the Russian ruler sanctioned the brazen nerve agent attack simply to goad Britain into a reaction that he can strike back against and look like a strongman standing up to the West to voters.

Former British Ambassador to Russia Sir Tony Brenton said yesterday: “The more Putin can point to Western hostility and aggression, the more he rallies the Russian people around him”.

Sir Tony added: “Russia is number one on a list of suspects that doesn’t include a number two”.

In a hint of action to come, the Chancellor said: “If there were to be an involvement of a foreign state, then obviously that would be very serious indeed and the government would respond appropriately.

Philip Hammond also told BBC1’s Andrew Marr Show that Britain will not be humiliated by the attack, that breaks every rule in the international book.

He added: “The vast resources that have been deployed and the high level assets that we have been able to use show that nobody is laughing at us.

“This is a very serious investigation. Let’s see where it leads us.”

Mrs May came under mounting pressure last night from campaigners and her own MPs to hit back at Russia.

Hero cop Sergeant Nick Bailey's car is removed by troops in Russian spy Sergei Skripal probe

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Senior Tory Jacob Rees-Mogg said Russia would become “a rogue state” if proof emerged it orchestrated the attack.

Commons Foreign Affairs Committee chairman Tom Tugendhat described Russia as “a great country that has been taken over by KGB thugs”.

It also emerged that the Cabinet’s two hawks – Foreign Secretary Boris Johnson and Defence Secretary Gavin Williamson - are pushing for the toughest response possible.

The pair want military reinforcements to be sent to Eastern Europe and provocative exercises by Royal Navy ships in the Black Sea.