Boris Johnson has hit out at the "torrent of absurdity" from Moscow following the Salisbury nerve agent attack - and accused Labour leader Jeremy Corbyn of being the Kremlin's "useful idiot".
The Foreign Secretary said the Kremlin was peddling an "avalanche of lies and disinformation" following the attack which left Russian double-agent Sergei Skripal and his daughter Yulia in hospital.
And he stepped up the Tory attack on Mr Corbyn, claiming the Labour leader was lending "false credibility" to the propaganda from Moscow by refusing to say "unequivocally" that the Russian state was responsible for the Salisbury incident.
A Labour spokesman hit back, claiming that Mr Johnson had "made a fool of himself and undermined the government" by misrepresenting the findings of the Porton Down laboratory on the source of the Novichok chemical agent.
Mr Skripal, 66, and his 33-year-old daughter Yulia were left fighting for their lives in hospital after being found unconscious on a park bench in Salisbury on March 4.
The former spy is said by medics to be improving rapidly and no longer in a critical condition while his daughter has said she is growing stronger by the day.
But the Foreign Office has said the pair are likely go have "ongoing medical needs" and thoughts in Whitehall have turned to what happens when they are well enough to leave hospital.
The Sunday Times reported that the Skripals could be offered new identities and a life in the USA, while the Sunday Telegraph suggested they could be placed under a witness protection scheme.
Writing in the Sunday Times, Mr Johnson accused Mr Corbyn of supporting the propaganda campaign launched by Vladimir Putin's government.
"There is only one thing that gives the Kremlin succour and lends false credibility to its propaganda onslaught. That is when politicians from the targeted countries join in.
"Sadly, I am driven to the conclusion that Jeremy Corbyn has joined this effort."
The Foreign Secretary said the Labour leader was playing "Putin's game" and "shames himself by lending it succour".
But a Labour spokesman responded: "Jeremy Corbyn has repeatedly said the evidence points to Russia being responsible, directly or indirectly, and that the Russian authorities must be held to account on the basis of evidence.
"Boris Johnson has made a fool of himself and undermined the Government by seriously misrepresenting what he was told by Porton Down chemical weapons experts.
"These ridiculous insults won't distract attention from the fact that he has clearly misled the public over vital issues of national security."
Mr Johnson's broadside in the Sunday Times came after Russia formally requested a meeting with him to discuss the Skripal case.
The Russian government said it hoped the UK would "engage constructively" with the request for ambassador Alexander Yakovenko to have face-to-face talks with Mr Johnson.
But the move was branded a "diversionary tactic" by the Foreign Office.
In a statement posted on its website on Saturday, the Russian Embassy said "interaction" between it and the Foreign Office was "utterly unsatisfactory".
They added: "We believe that it is high time to arrange a meeting between Ambassador Alexander Yakovenko and Foreign Secretary Boris Johnson in order to discuss the whole range of bilateral issues, as well as the investigation of the Salisbury incident.
"Ambassador Yakovenko has already sent a respective personal note to the Foreign Secretary.
"We hope that the British side will engage constructively and that such meeting is arranged shortly."
Moscow has denied being responsible for the poisoning of the Skripals but the incident has plunged diplomatic relations between Russia and the West into the deep freeze.
A Foreign Office spokesman said: "It's Russia's response that has been unsatisfactory.
"It's over three weeks since we asked Russia to engage constructively and answer a number of questions relating to the attempted assassinations of Mr Skripal and his daughter.
"Now, after failing in their attempts in the UN and international chemical weapons watchdog this week and with the victims' condition improving, they seem to be pursuing a different diversionary tactic.
"We will of course consider their request and respond in due course."
Whitehall sources said Russian foreign minister Sergey Lavrov had turned down the chance for discussions and dismissed the embassy's move as the "latest in a series of Russian disinformation attempts".