Jeremy Corbyn is facing growing discontent within his own party over his stance on Russia, after he repeatedly called for further evidence before condemning the state for the attack on Sergei Skripal earlier this month.
The Labour leader refused to condemn Russia over the attack following Theresa May's claim that it was "attempted murder" conducted on behalf of the Russian state.
May unveiled a number of measures in retaliation against the attack, which took place in Salisbury earlier this month. They include expelling 23 diplomats, who she claimed were in fact "undeclared intelligence agents", and a partial boycott of the World Cup, meaning no ministers or members of the Royal Family will attend this summer.
But while Corbyn condemned the act, he skirted from blaming the Russian state. Instead he queried whether the UK had met its obligations under the Chemical Weapons Convention in allowing Russia access to a sample of the nerve agent - parroting comments made by Russia's foreign minister Sergey Lavrov yesterday, which had already been dismissed by the government.
The leader of the opposition added that it was "a matter of huge regret" that the UK diplomatic capacity had been stripped back over the past five years.
He told MPs "our response must be decisive and proportionate and based on clear evidence".
Numerous Labour backbenchers offered the Prime Minister their support and condemned Russia - including Chris Bryant, Hilary Benn, Margaret Hodge, Yvette Cooper, Ben Bradshaw and Pat McFadden during the course of a two-hour debate in the Commons.
But Corbyn's spokesman insisted there was still a lack of evidence categorically linking Russia with the attack.
He noted that there was a "history in relation to weapons of mass destruction and intelligence that is problematic, to put it mildly" - alluding to the claims that led to the invasion of Iraq under former Labour Prime Minister Tony Blair.
The spokesman said: "Clearly whoever carried out the attack is responsible for what was a completely heinous and reckless act."
He echoed comments made by Corbyn that the agent could have fallen into a third party's hands, saying “The break up of the Soviet state led to all sorts of material ending up in random hands".
But Labour MPs slammed the spokesman's words.
Ilford South MP Mike Gapes said: "Well Seumas [Milne] has form on these matters," pointing to articles he wrote as a Guardian columnist in defence of Russia over the 2015 murder of Boris Nemtsov.
In response to a tweet quoting Milne, Luton South MP Gavin Shuker said: "This once great party."
Labour MPs were so outraged, many including Chuka Umunna, Stella Creasy, Alison McGovern and Ruth Smeeth signed an early day motion tabled by John Woodcock stressing the house "unequivocally accepts the Russian state's culpability for the poisoning of Yulia and Sergei Skripal."
Rumours flying around Westminster suggested that at least one member of the shadow Cabinet was prepared to resign over the matter.
Corbyn issued another statement later this evening, in which his stance appeared to soften, although he stopped short of appprtioning blame absolutely.
"The Russian authorities must be held to account on the basis of the evidence and our response must be both decisive and proportionate," he said.