In a resignation letter to the Labour leader, the Barrow and Furness MP protested that Mr Corbyn could not return the party to being the “inclusive mainstream, progressive force my constituents desperately need”.
In his letter, he told Mr Corbyn he was resigning “following your refusal to appoint an independent investigator to rule on my disciplinary case and in the light of clear evidence that the process has been manipulated for factional purposes”.
But he added that Mr Corbyn had made Labour “unfit” for office and “would pose a clear risk to UK national security as prime minister”.
“The party for which I have campaigned since I was a boy is no longer the broad church it has historically been,” he wrote.
“Antisemitism is being tolerated and Labour has been taken over at almost every level by the hard left, far beyond the dominance they achieved at the height of 1980s militancy.”
Mr Woodcock said that, as an independent, he would be prepared to vote with Theresa May when he agreed with her policies.
A Labour source strongly denied Mr Woodcock’s claim that his case had been “manipulated”, insisting it was being investigated in line with normal rules and procedures.
The inquiry – because of his resignation – would now be abandoned, denying the complainant the right to have their allegation of sexual harassment heard, the source said.
However, in his letter the MP wrote: “I strongly deny the charge made against me but am committed to the complaint being thoroughly and fairly investigated.
“I will now seek to refer myself to an independent process so the case can be properly heard.”
In the briefest possible statement, a Labour spokesperson said: “Jeremy thanks John for his service to the Labour party.”
But the Labour source said: “The process is the same for everyone. There is no political involvement in these processes.”
Mr Woodcock was accused of sending inappropriate texts and emails to a former member of staff from 2014 to 2016.
A former aide to Gordon Brown, Mr Woodcock has been an outspoken critic of Mr Corbyn’s leadership – clashing with him over nuclear weapons, Russia and antisemitism.
At the 2017 general election, he pledged he would not vote to put him into 10 Downing Street.
In his attack on Mr Corbyn’s leadership, Mr Woodcock said: “There is little chance of returning the Labour party to the inclusive, mainstream electoral force my constituents desperately need.
“In these circumstances, I can no longer justify engaging in a rigged process to be readmitted to it.”
Mr Woodcock said he would “continue to give my all to the people of Barrow and Furness as an independent MP on the opposition benches”.
“My loyalty to them always comes first, so I will work with the government when it is trying to do the right thing, and will also work with the many good colleagues who are still trying to do their best in Labour,” he said.
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