BRITAIN is to step up its efforts to counter the lethal threat from Russia’s GRU military spy network, Theresa May has told MPs, after she dramatically announced that the two men suspected of the “despicable” Salisbury poison attack were members of it.

Alexander Petrov and Ruslan Boshirov arrived in Britain on a flight from Moscow on Friday March 2 and stayed in a low-key east London hotel, travelling the next day via the Underground and Waterloo station to Salisbury on a reconnaissance mission.

On Sunday March 4, they made the same journey and are believed to have smeared the Novichok nerve agent on the front door handle of the home of Sergei Skripal, himself a former GRU agent. Within hours, the two suspects were on a plane back to Russia. Their names are thought to be aliases.

But Mr Skripal, 67, and his daughter Yulia, were taken ill in Salisbury city centre and spent weeks in hospital, fighting for their lives before eventually recovering and being discharged.

The Prime Minister praised the “painstaking and methodical” work of the police and the security services. She explained how some 250 detectives had trawled through more than 11,000 hours of CCTV footage and taken more than 1,400 statements.

She said the forensic investigation had produced sufficient evidence for charges to be brought against the two Russian nationals, including for conspiracy to murder Mr Skripal, for his attempted murder and that of his daughter Yulia and of Detective Sergeant Nick Bailey and the use and possession of Novichok.

The two Russians are now also the prime suspects in the case of Dawn Sturgess, 44, and her partner Charlie Rowley, 48, who handled the perfume bottle, which contained the nerve agent. Both were hospitalised but Ms Sturgess later died.

In a Commons statement Mrs May said: “We repeatedly asked Russia to account for what happened in Salisbury in March and they have replied with obfuscation and lies.”

This, she said, included trying to pass the blame for the attack onto terrorists, international partners, and even Ms Skripal’s future mother-in-law.

“They even claimed that I, myself, invented Novichok. Their attempts to hide the truth by pushing out a deluge of disinformation simply reinforces their culpability.”

The PM stressed how the GRU was “not a rogue operation. It was almost certainly also approved outside the GRU at a senior level of the Russian state”.

She made clear the UK would continue to engage with Russia on peace and security but would also “make it clear there can be no place in any civilised international order for the kind of barbaric activity we saw in Salisbury in March”.

Mrs May said while she could not go into detail, the UK would with allies deploy the “full range of tools from across our national security apparatus to counter the threat posed by the GRU”.

She added: “We were right to act against the Russian state in the way we did, and we are right now to step up our efforts against the GRU. We will not tolerate such barbaric attacks against our country. Together with our allies, this Government will continue to do whatever is necessary to keep our people safe.”

Jeremy Corbyn insisted the use of military nerve agents on the streets of Britain was an “outrage and beyond reckless” and called on the Russian Government to “give a full account of how this nerve agent came to be used in the UK”.

But Boris Johnson, the former Foreign Secretary, took the Labour leader to task for his “weaselly language…in failing to condemn what is now incontrovertible in the eyes of all right-thinking people: involvement of the Russian state at the highest level in the Salisbury poisonings".

Ian Blackford for the SNP said the arrest warrants would send a “clear message that all of us here will not tolerate the behaviour from the Russians that took place in Salisbury”.

He added: “The threat from Russia must always be met by a united front from all of us together standing in solidarity against the abuse of power.”

The PM thanked Mr Blackford for his “clear condemnation of the Russian state,” adding: “I only wish such a clear condemnation might be possible from the leaders of all parties in the House.”