THERESA May has denied pandering to the whims of Donald Trump over the Syrian airstrikes as UK and US spy chiefs warned that Russia was preparing to mount revenge cyber-attacks on Britain’s “critical infrastructure”.

In a Commons statement, the Prime Minister also accused Moscow of helping the Syrians block weapons inspectors from visiting the site of the poison gas attack in Douma and of trying to “conceal the facts of the attack”; a claim denied by the Kremlin.

In an unprecedented move, the UK National Cyber Security Centre [NCSC] together with the FBI and the US Department of Homeland Security issued a joint “technical alert,” setting out the Russian cyber-threat across the public and private sectors.

Theresa May: Moscow blocking weapons inspectors from visiting Douma

They said the Russian Government’s campaign to exploit internet devices “threatens our respective safety, security and economic well-being”. Fears have been raised that Russian state hackers could disrupt Britain’s power supplies, transport links and health services.

Officials said the UK-US cyber-alert had been planned for “some time” and was not directly related to the weekend missiles strikes on Syria.

But Ciaran Martin, the NCSC’s Chief Executive, said it was a “significant moment” in the fightback against Russian aggression in cyberspace.

He said security services had seen the “sustained targeting of multiple entities” over a series of months with millions of machines around the word being targeted.  Kremlin-backed hackers, Mr Martin explained, were using “compromised routers” to conduct spoofing “man-in-the-middle” attacks to “support espionage...and potentially lay a foundation for future offensive operations”.

Fake News? How TV tells Russians that Syria chemical attacks were 'staged'

Last night, a UK Government spokesman said the Kremlin-backed cyber-activity was yet another example of Russia’s “disregard for international norms and global order; this time through a campaign of cyber-espionage and aggression, which attempts to disrupt governments and destabilise business”.

He stressed the attribution of Moscow’s “malicious activity” sent a clear message to Russia: “We know what you are doing and you will not succeed.”

Earlier in the Commons, Mrs May told MPs the military action against the Assad regime was legally and morally right to degrade its chemical weapons capability and to deter any future use.

“This was not about intervening in a civil war and it was not about regime change. It was about a limited, targeted and effective strike that sought to alleviate the humanitarian suffering of the Syrian people by degrading the Syrian regime’s chemical weapons capability and deterring their use,” she declared.

The PM argued that the allied forces could not wait for the weapons inspectors to go into Douma as the Russians had already sought to stop any investigation and were already blocking inspectors on the ground in Syria from examining the site.

   “The regime has reportedly been attempting to conceal the evidence by searching evacuees from Douma to ensure they are not taking out the region samples that could be tested elsewhere. And a wider operation to conceal the facts of the attack is underway supported by the Russians,” explained Mrs May.

She denied Britain was “just following orders from America,” telling MPs: “Let me be absolutely clear: we have acted because it is in our national interest to do prevent the further use of chemical weapons in Syria and to uphold and defend the global consensus that these weapons should not be used.”

Theresa May: Moscow blocking weapons inspectors from visiting Douma

On the issue of recalling Parliament, the PM insisted this was an emergency and to protect life and the safety of Britain’s forces swift action was called for.

Jeremy Corbyn said the chemical attack on Douma was “horrific” but argued the military action was “legally questionable”.

In an at times acrimonious atmosphere, he faced shouts of “shame” from Tory MPs as he told the Commons: “This statement serves as a reminder that the Prime Minister is accountable to this Parliament, not to the whims of the US President.”

The Labour leader insisted a War Powers Act was needed to give Parliament the power to “support or stop the Government from taking planned military action”.

He suggested that any military action needed United Nations approval but Mrs May stressed how because of Russia’s use of veto she was not prepared for Moscow to be able to veto UK foreign policy.

Her Tory colleague Dominic Grieve, the former Attorney General, suggested Mr Corbyn’s approach would mean any tyrant with the backing of an amoral state within the Security Council could commit genocide with impunity.

“In those circumstances, far from upholding the international rules-based system, the reality is that it would be dead,” insisted the Conservative backbencher.

Ian Blackford for the SNP argued that it was “perfectly possible” for the PM to have recalled Parliament in advance of Saturday’s air strikes.

He asked: “Have the Government learned nothing from the Chilcot review? Once again we have been dragged into military action with little regard for the humanitarian situation on the ground and no long-term strategic plan.”

The Highland MP insisted: “There is no military solution to the crisis; the solution must be political.

The PM spent more than three hours on her feet, taking questions from 140 backbenchers as well as party leaders.  Later, the Speaker granted a so-called three-hour SO24 debate but which did not have a substantive motion to vote on.  Another three-hour debate was granted to Mr Corbyn for Tuesday so MPs could consider MPs’ rights to debate and approve military action overseas.