Union leaders and representatives of the various factions in the Labour Party are set to meet on Sunday in an attempt to break the deadlock over Jeremy Corbyn's leadership.

Unite general secretary Len McCluskey has been leading efforts to find a way out of the impasse, holding talks in recent days with Mr Corbyn, his deputy Tom Watson and representatives of the Parliamentary Labour Party (PLP).

The embattled Labour leader has refused to step down despite facing an overwhelming vote of no confidence by Labour MPs and mass resignations in his shadow cabinet, repeatedly citing his popular support at the party's grass roots.

Around 130,000 members have joined Labour in the past fortnight - taking the membership up to 515,000 - although it is not clear whether they have signed up to back Mr Corbyn or to support efforts to remove him.

Representatives from Unite and the other main unions affiliated to Labour are set to meet with Mr Watson, PLP chairman John Cryer and chief whip Rosie Winterton but also with Mr Corbyn's allies John McDonnell, the shadow chancellor and the leader's communications chief Seumas Milne, Channel 4 News reported.

A union source told the Press Association the meeting, planned to take place ahead of Unite's policy conference in Brighton, would mean "the three main parts of the Labour Party for the first time coming together on this".

The plans for a crisis meeting emerged after Mr Corbyn's leadership of the Labour Party was backed by a major union, but it stressed that the party must function as an "effective opposition".

A motion passed by Unison's Labour Link conference in Newcastle called for a way forward to be found to unite the party.

The Unison forum backed a motion agreeing to continue to "support Jeremy Corbyn with his anti-austerity platform and his belief in a new kind of politics that is progressive and fair in its outlook".

"Jeremy is the elected leader and Forum hopes that a way forward can still be found so that we have a united Party defending the interests of working people," the motion said.

"However, Forum also believes that the Labour Party, founded to advance the interests of working people, must function as an effective opposition and should appear as a government in waiting to the electorate."

Writing in The Guardian, Mr Corbyn repeated his challenge to opponents to stand against him in a leadership election.

"I have made clear I am ready to reach out to Labour MPs who oppose my leadership - and work with the whole party to provide the alternative the country needs," Mr Corbyn said.

"But MPs also need to respect the democracy of our party and the views of Labour's membership, which has increased by more than 100,000 to over half a million in the past fortnight alone - by far the largest it has ever been in modern times.

"Our priority must now be to mobilise this astonishing new force in politics, and ensure people in Britain have a real political alternative. Those who want to challenge my leadership are free to do so in a democratic contest, in which I will be a candidate."

Former shadow business secretary Angela Eagle has insisted she is ready to challenge Mr Corbyn if he refuses to stand down while Owen Smith, the ex-shadow work and pensions secretary, has said he is "ready to do anything I can to save and serve the party" amid speculation he was also considering a leadership bid.

Mr Corbyn has so far resisted calls to step down as leader after MPs voted by 172-40 that they had no confidence in him.