LONDON (Reuters) - British Labour leader Jeremy Corbyn warned on Friday against rushing into a new Cold War with Russia before full evidence of Moscow’s culpability in a military-grade nerve toxin attack on a former double agent is proven.

The leader of the Labour Party Jeremy Corbyn responds to Britain's Prime Minister Teresa May's address to the House of Commons on her government's reaction to the poisoning of former Russian intelligence officer Sergei Skripal and his daughter Yulia in Salisbury, in London, March 14, 2018. Parliament TV handout via REUTERS

Prime Minister Theresa May said Russia was behind the Novichok nerve agent attack on Sergei Skripal, a former colonel in Russian military intelligence who betrayed dozens of Russian agents to Britain.

Skripal and his daughter Yulia have been critically ill in hospital since March 4 when they were found slumped unconscious on a bench outside a shopping center in the English city of Salisbury. A British policeman was also injured.

After the first known offensive use of such a weapon on European soil since World War Two, May gave 23 Russians who she said were spies working under diplomatic cover at the London embassy a week to leave.

But Corbyn, who has been criticized for taking a much more cautious approach to the poisoning, said that rushing ahead of the evidence in a fevered atmosphere did not serve national security.

“To rush way ahead of the evidence being gathered by the police, in a fevered parliamentary atmosphere, serves neither justice nor our national security,” he wrote in an article in the Guardian newspaper.

“This horrific event demands first of all the most thorough and painstaking criminal investigation.”

The 68-year-old socialist leader said Labour did not support Putin and that Russia should be held to account if it was behind the attack.

“That does not mean we should resign ourselves to a ‘new cold war’ of escalating arms spending, proxy conflicts across the globe and a McCarthyite intolerance of dissent,” Corbyn said.

Corbyn suggested that the Russian mafia, which he said had been allowed to gain a toehold in Britain, might be behind the attack and said Britain should stop accepting corrupt money from the former Soviet Union.

“We must stop servicing Russian crony capitalism in Britain, and the corrupt billionaires who use London to protect their wealth,” he said.

“We agree with the government’s action in relation to Russian diplomats, but measures to tackle the oligarchs and their loot would have a far greater impact on Russia’s elite than limited tit-for-tat expulsions.”

Corbyn was once written off by both his own party and May’s Conservatives, but his unexpectedly strong result in last year’s national election has convinced many of Labour’s opponents that Corbyn is a potential prime minister if May’s government falls.