'Don't threaten us': Russia's extraordinary nuclear warning to May

• Russia warns against ‘threatening a nuclear power’

• Trump leads allies’ backing of Britain and says ‘we’ll back you all the way’

• May ‘s midnight deadline for Russia passes in stalemate

• Hundreds of Salisbury residents warned they could have contaminated clothing

• Russian spy Sergei Skripal and his daughter Yulia still alive

Russia has warned Britain to “consider the consequences” of mounting a retaliatory cyber strike and told Theresa May not to threaten a nuclear power.

The Prime Minister is preparing to chair a meeting of the national security council after the midnight deadline she set Moscow over the spy poisoning case passed. She has pledged to set out a “full range” of measures to be taken in response if there is no credible response from the Kremlin.Russia said on Tuesday it would ignore demands for an explanation over how a nerve agent was deployed in Salisbury unless Britain agreed to send it samples of the poison.

In a fresh sign of the escalating diplomatic tension sparked by the case, the Russian embassy in the UK also fired off a salvo of tweets warning the threat of sanctions would “meet with a response”.

On a fast-moving day of developments and the ratcheting up of diplomatic tensions, Russian foreign ministry spokeswoman Maria Zakharova said on Rossiya 1 state TV: “One should not threaten a nuclear power”, particularly, she added, in light of remarks made by Putin earlier this month in which he announced an array of new weapons.

She added: “When an foreign affairs body of a country is headed by people who have absolutely nothing to do with foreign policy, who built their career on populism…, it is normal for them to come out and start scare-mongering. Do not (try to) scare us,” apparently referring to Boris Johnson.

The UK Government has not publicly disclosed the options under consideration if Russia fails to meet its deadline, but reports on Tuesday suggested one possibility was a cyber counter-attack.

Responding to the speculation, the Russian Embassy in the UK issued extraordinary series of tweets: “Statements by a number of MPs, ‘Whitehall sources’ and ‘experts’ regarding a possible ‘deployment’ of ‘offensive cyber-capabilities’ cause serious concern.

“Not only is Russia groundlessly and provocatively accused of the Salisbury incident, but apparently, plans are being developed in the UK to strike Russia with cyber weapons.

“Judging by the statements of the Prime Minister, such a decision can be taken at tomorrow’s meeting of the National Security Council.

“We invite the British side to once again consider the consequences of such a reckless move.”

On Tuesday, the developments came thick and fast.

Allies back Britain

Britain’s international allies, led by the US, have responded with condemnation over the nerve agent attack.

Mrs May was assured of the backing of the US, Germany and France in calls to President Donald Trump, German Chancellor Angela Merkel and French President Emmanuel Macron, according to Downing Street.

Mr Trump told Mrs May that “the US was with the UK all the way, agreeing that the Russian government must provide unambiguous answers as to how this nerve agent came to be used”.

And the Baltic states, which border Russia, also offered their support in the wake of the attack.

Latvia said it was prepared to offer the “required support” and urged Nato and the EU to agree on action.

Second Russian death

In a further extraordinary development, a probe has been launched by counter-terrorism police amid reports a Russian exile who was a close friend of Putin critic Boris Berezovsky has been found dead.

Scotland Yard said a man in his 60s was found at a home in Clarence Avenue, New Malden, south-west London on Monday and that the cause of his death is unexplained.

The force said in a statement: “At this stage the Met Police Counter Terrorism Command is leading the investigation as a precaution because of associations that the man is believed to have had.

“There is no evidence to suggest a link to the incident in Salisbury.”

Lawyer Andrei Borovkov told Russian media outlets that his client, Nikolai Glushkov, the former deputy director of airline Aeroflot, had died.

But he said he was unaware of the time and circumstances.

Nerve agent warning

Beyond Mr Skripal and his daughter, Detective Sergeant Nick Bailey, one of the first responders to the incident, remain in hospital.

Thirty-five local residents have also been seen in hospital. Thirty-four have been released while one is still being monitored.

Separately, one of the inventors of the nerve agent has warned that tiny traces of the chemical could put hundreds of people at risk for years to come.

Dr Vil Mirzayanov was part of the team that developed Novichok in a Russian chemical weapons institute.

He later became so concerned about the damage it could cause he became a whistleblower and fled to America.

‘It’s the same as nerve gas but 10 times, at least 10 times, more powerful,’ he told Sky News.

The chemist warned that symptoms could develop even years after exposure to the substance, and that there is no cure.

Russia hits back

Russia had previously reiterated its innocence over the poisoning, saying Moscow is ‘not to blame’ for the nerve agent attack.

Russian Foreign Minister Sergei Lavrov warned that Moscow will only co-operate with Britain on the investigation if it receives samples of the nerve agent that is believed to have been used to target Mr Skripal and his daughter.

Mr Lavrov said that requests to see samples of the nerve agent have been turned down, which he called a violation of the Chemical Weapons Convention, which outlaws the production of chemical weapons.

In a separate astonishing outburst on Tuesday morning, one Russian MP said that the PM herself was behind the attempted murder, comparing Mrs May to Hitler.

May makes her move

In a startling statement on Monday evening aimed directly at the Kremlin, the Prime Minister said it was ‘highly likely’ Russia was responsible for the attempted murder of the former spy, calling it a ‘reckless’ act.

A failure by Russia to provide a “credible response” would lead her to view the attack in Salisbury as “an unlawful use of force by the Russian State against the United Kingdom”, sparking undefined retaliatory measures.

Russia responded almost immediately, however, describing Britain’s reaction as a ‘circus show’.

‘There are therefore only two plausible explanations for what happened in Salisbury on the 4th of March,’ the PM said.

‘Either this was a direct act by the Russian State against our country or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others.’

President Vladimir Putin himself responded to a direct question over Russia’s involvement by saying: ‘You should first get things clear yourselves on the spot and after that we will discuss this with you.”

Boris Johnson had previously told the Russian ambassador that Moscow must ‘immediately provide full and complete disclosure’ of its Novichok nerve gas programme to the Organisation for the Prohibition of Chemical Weapons.

On Monday, the chairman of the Foreign Affairs committee said the attempt on Mr Skripal’s life was ‘looking awfully like it was state-sponsored attempted murder’.

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The Government is under increasing pressure to take a tough line on the Kremlin if it can prove it was involved in the attack.

The expulsion of Russian diplomats and spies, new financial sanctions against individuals linked to the Kremlin, and withdrawal of official representation from this summer’s World Cup are among the retaliatory measures which could be on the table if Britain takes action.

Earlier a Tory former defence minister said Britain could be entering “a period of cool war” with Russia.

Mark Francois urged Theresa May “to look again at our ability to deter Russia” as he made a fresh plea for greater defence spending.

Mr Francois, having commended the Prime Minister for her statement to the Commons, said: “Would she also accept that while we may not be in a period of cold war with Russia, as we were in the 1980s, because of their actions, it could be said that we are at least now entering a period of cool war.

Up to 500 people in Salisbury were told to wash their clothes and personal items today, a week after the attack.

The advice was met with ire from residents, who were angry that health officials waited seven days before telling them to take precautions after Mr Skripal, 66, and his daughter, 33, collapsed on a bench in the Wiltshire city.