Jeremy Corbyn has cast doubt on evidence that led the Government to blame Russia for the Salisbury attack, pointing instead to the “WMD” saga before the Iraq War as reason to be suspicious of Theresa May’s approach.

After the Labour leader refused to blame Moscow in the Commons, his spokesman said ministers’ use of intelligence on Iraq’s weapons programmes in 2003 meant accepting the Government’s position on Russia now is “problematic”.

But his position sparked a furious with Labour MPs who first stood to take an overtly different line in the Commons and then took action outside the Chamber to set themselves apart.

Mr Corby condemned the “appalling act of violence” on 4 March which left ex-Russian spy Sergei Skripal, his daughter and a policeman in a serious condition, but then urged continued “robust dialogue” with Moscow.

But after being asked why Mr Corbyn would not overtly state that Russia was culpable, his spokesman said: “Obviously the Government has access to information and intelligence on this matter which others don’t.

"However, also, there’s a history in relation to weapons of mass destruction and intelligence which is problematic to put it mildly.”

The spokesman added: “If you remember back to the WMD saga, there was both what was actually produced by the intelligence services, which in the end we had access to and then there was how that was used in the public domain in politics.

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“So there is a history of problems in relation to interpreting that evidence, but in this case obviously the Government may well have other evidence that we are not aware of.”

Russian Foreign Minister Sergei Lavrov has said the UK is bound to provide a sample of the nerve agent used in the attack to Russian investigators under international treaties, something Ms May has withheld.

There’s a history in relation to weapons of mass destruction and intelligence which is problematic to put it mildly Jeremy Corbyn’s spokesman

But Mr Corbyn’s spokesman appeared to back the move, saying: “The right approach is to seek the evidence, to follow international treaties, particularly in relation to prohibited chemical weapons. This was a chemical weapons attack carried out on British soil.

“There are procedures that need to be followed in relation to that and the rule of law.”

Mr Corbyn’s spokesman accepted that there is evidence showing that it is highly likely the weapons-grade nerve agent was manufactured in Russia or in the former Soviet Union.

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He explained that senior Labour figures had attended briefings from the intelligence services, but pointed towards an alternative explanation for the incident other than direct Russian responsibility.

The spokesman said even the Prime Minister had said there may be two explanations, with one being that the chemical had fallen into the wrong hands.

He said: “In relation to the second alternative explanation, in other words the loss of control of military grade nerve agent, we highlighted and have done repeatedly the dangers of mafia-like groups and Russian oligarchic interests in London and their links with elements of the Russian state and that we need to take firm action on that and Jeremy highlighted that point in his response.”

Earlier in the Commons, Labour MP Yvette Cooper, chairwoman of the Home Affairs Select Committee, was among those who differentiated herself from the leader’s position.

She said Russia’s actions must be met with “unequivocal condemnation”, while long-time Corbyn critic John Woodcock said: “This is a day for the House to speak as one for the nation, and (Ms May) will be reassured to hear that a clear majority of Labour MPs, alongside the leaders of every other party, support the firm stance which she is taking.”

Russian MP compares Britain to Hitler over the Salisbury nerve agent attack

Labour former minister Pat McFadden earlier told the Chamber: “Responding with strength and resolve when your country is under threat is an essential component of political leadership.

“There is a Labour tradition that understands that and it has been understood by prime ministers of all parties who have stood at that despatch box.

“That means when chemical weapons are used, we need more than words, but deeds.”

Backbenchers Mike Gapes, Chris Leslie and Stephen Doughty also made comments supportive of Ms May’s stance.

Labour backbencher John Woodcock tabled an Early Day Motion, a ort of parliamentary petition, “unequivocally” accepting the “Russian state’s culpability” for the attack, and supporting “fully” the statement made by Ms May in the Commons.

The motion was swiftly signed by a number of prominent critics of Mr Corbyn, some of whom went public with their criticism of the leader’s senior spokesman Seumas Milne.

Labour MP Anna Turley tweeted: “I’m afraid Seumas doesn’t speak for my Labour or British values”, while Chuka Umunna said: “Mr Milne’s comments do not represent the views of the majority of our voters, members or MPs”.

But responding, Mr Milne was defiant, saying: “In these kinds of crisis there are often initial reactions which aren’t necessarily later backed up by reality or fact.