Labour deputy leader Tom Watson is to hold emergency talks with trade union leaders in a last ditch attempt to end the impasse over Jeremy Corbyn's leadership.
At a one-to-one meeting at Westminster on Monday, Mr Watson told Mr Corbyn he could not carry on as party leader without the backing of the party's MPs who last week voted overwhelmingly in favour of a vote of no confidence in him.
However, he told a packed meeting of the Parliamentary Labour Party that Mr Corbyn had again made it clear that he had no intention of walking away, issuing a renewed appeal to supporters to unite behind his leadership.
In the wake of the failure of this latest attempt to break the deadlock, Labour sources said that union leaders had "reached out" to Mr Watson to see if they could find a negotiated settlement.
"It is the last throw of the dice," the deputy leader told MPs.
Separately Mr Watson met former shadow business secretary Angela Eagle and ex-shadow work and pensions secretary Owen Smith, who are both considering a challenge to Mr Corbyn if he continues to resist calls to go.
Both were said to have agreed to hold back while there was still a chance of a negotiated settlement which would see Mr Corbyn finally walk away.
"They accept that is the right thing to do while there is a chance of some kind of deal," one source said.
"Tom said he is aware the window is closing very rapidly. The Parliamentary Labour Party have made their views very clear. I don't think they will regard any settlement that sees Jeremy remain in place as being acceptable."
In a video posted on the internet, Mr Corbyn insisted he was carrying on with the responsibility given to him when elected leader by an overwhelming majority of grass roots members and called for the party to "come together".
He brushed away claims he only half-heartedly campaigned for EU membership in the referendum and so contributed to the vote for Brexit - which triggered the current crisis - pointing out that two thirds of Labour voters backed Remain.
He said the membership "wants and expects" everyone in the party - including MPs - "to work together in their interests".
Earlier, Ms Eagle made it clear she was ready to mount a leadership challenge if Mr Corbyn did not step down.
However the fear for the rebels seeking to oust Mr Corbyn is that if they do put up a challenger he could still win in a ballot of grass roots activists leaving him even more strongly entrenched in his position.