JEREMY Corbyn last night vowed to fight on as Labour leader after his former shadow cabinet colleague Angela Eagle confirmed she would challenge him for the job.

Eagle, who resigned as shadow business secretary last month, announced she would launch her formal leadership campaign on Monday.

She said Corbyn had “failed to fulfil his first and foremost duty” - to lead an effective party that could hold the government to account and present itself as a credible alternative.

Owen Smith, who quit as work and pensions spokesman, and is also considering a leadership bid, warned Labour was facing its “greatest crisis in generations” and could split.

There is now likely to be an intense legal argument over whether Corbyn is entitled to a place on the ballot paper, as he cannot muster the threshold support of a fifth of MPs.

His opponents' best chance to topple him is to exclude him, as if he does appear as the incumbent, he may well be re-elected by the same activists who overwhelmingly backed him last year.

Eagle’s statement came after Labour deputy Tom Watson said union-brokered compromise talks over Corbyn’s future had failed because of the leader’s refusal to give ground.

Watson said that “with regret and profound sadness” he had concluded that Corbyn’s declaration that he would continue “come what may” meant there was “no realistic prospect of reaching a compromise" over his future role in the party.

Watson said the 172-40 vote of no confidence in Corbyn by Labour MPs on June 28 showed he had “lost the support of the PLP with little prospect of regaining it".

He added: “If circumstances change I hope talks can be resumed."

Corbyn’s spokesman said it was "disappointing" that Watson had walked away from efforts to end the stand-off between Corbyn and his MPs, most of whom want him to quit.

He said: "Jeremy is committed to fulfilling all his responsibilities as democratically elected leader and will not betray the hundreds of thousands of people who elected him for a different direction for the Labour Party and a different kind of politics.

"He will remain leader of the Labour Party and will contest any leadership challenge if one is mounted."

Since the Brexit vote on June 23, Corbyn has been disowned by 80 per cent of his MPs, who regard him as electoral poison, but has refused to resign, citing the 59 per cent support he received in the ballot of Labour members just ten months ago.

The collapse of the talks, set up by Unite general secretary Len McCluskey, prompted Eagle to show her hand after mounting speculation that she would stand.

She thanked the union movement, Watson, PLP chair John Cryer and chief whip Rosie Winterton for trying "to find a solution to the impasse Labour faces with a leader who has failed to fulfil his first and foremost duty, that is to lead an organised and effective Parliamentary Labour Party that can both hold the Government to account and demonstrate we are ready to form a government in the event of a general election.

“On Monday morning I will announce my candidature for leader of the Labour Party. I will explain my vision for the country and the difference a strong Labour Party can make.”

McCluskey said he had received no advance notice of Watson's exit from the talks, and called it an "act of sabotage fraught with peril for the future of the party".

A workable plan “had never seemed closer” McCluskey said, warning: “Should there have to be a leadership election, I must warn that any attempts to keep Jeremy Corbyn, elected just 10 months ago with an enormous mandate, off the ballot paper by legal means risks a lasting division in the party.

"It is time for everyone to commit to a democratic and dignified procedure as the only way to avert such a disaster for working people."

Shortly before Eagle's announcement, Corbyn had made a doomed appeal for the party to “come together” while attending the Durham Miners' Gala and insisted he was “very happy” as leader.

Addressing thousands of supporters, he said there was "no pressure on me, none whatsoever" compared to the pressure of poverty, and suggested he would return as prime minister.

"I consider it the duty, whoever holds the office of leader of the Labour Party, to be at the Durham Miners' Gala. And so, we will all be here together when we have elected a Labour government in Britain."