"Either this was a crime authored by the Russian state; or that state has allowed these deadly toxins to slip out of the control it has an obligation to exercise," he wrote.

"If the latter, a connection to Russian mafia-like groups that have been allowed to gain a toehold in Britain cannot be excluded."

He added: "To rush way ahead of the evidence being gathered by the police, in a fevered parliamentary atmosphere, serves neither justice nor our national security."

The left-wing leader has drawn criticism from his own MPs for failing to fully back the Conservative government, which said Moscow was "culpable" for the March 4 attack.

Corbyn condemned the "barbaric" incident, which left Skripal and his daughter in a critical condition and also injured a police officer.

"But in my years in parliament I have seen clear thinking in an international crisis overwhelmed by emotion and hasty judgements too many times," he said, noting the flawed intelligence used to justify the US-led invasion of Iraq.

He said Labour was "no supporter of the Putin regime", but "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".

There are many Labour MPs who oppose Corbyn's left-wing views, but there has been a truce since he led the party to a better than expected result in last year's election.

His stance on Russia has put them in conflict once again, and by Friday morning, 33 had signed a parliamentary motion blaming Russia "unequivocally" for the attack.