Jeremy Corbyn's grip on the Labour leadership looked increasingly weak as Angela Eagle became the most senior member of his shadow cabinet to quit.

Ms Eagle, the shadow first secretary of state who deputises for Mr Corbyn at Prime Minister's Questions, said "we need a leader who can unite rather than divide the Labour Party".

Shadow housing minister John Healey, shadow energy secretary Lisa Nandy and shadow work and pensions secretary Owen Smith have all resigned - adding to the 12 shadow cabinet members Mr Corbyn lost on Sunday.

Mr Corbyn has been warned he will face a leadership contest but has vowed to fight on, relying on the support of grassroots members even though he enjoys little backing from his MPs and peers.

In her resignation letter Ms Eagle, the shadow business secretary, told Mr Corbyn: "It is time for you to stand aside."

She said: "It is with the greatest of sadness that, after nine months of trying to make your leadership work and despite your considerable personal qualities, I have come to the conclusion you are not the right person to lead the party we both love.

"You have lost the confidence of your colleagues, and you have struggled to win the confidence of our voters and the wider public."

In a joint statement Ms Nandy and Mr Smith told Mr Corbyn that a leadership contest was "inevitable" and called for deputy leader Tom Watson to take temporary charge of the party.

Mr Corbyn has vowed to fight any challenge to his position and Ms Nandy is understood to be considering a bid the leadership herself.

Ms Nandy and Mr Smith said: "It has become clear that he is unable to form a broad, inclusive shadow cabinet that draws on the best of our movement's left and right traditions.

"For that reason we have told Jeremy that whilst the party holds a leadership contest - which is now inevitable - we believe Tom Watson ought to take over as a caretaker leader to stabilise the party and to enable us to play a full part as the official opposition in one of the most difficult periods this country has ever faced."

Their decision came after leading a group of senior frontbenchers, including Mr Healey, Nia Griffith and Kate Green, for talks with Mr Corbyn.

"We had hoped to leave that meeting with the confidence to continue to support the leadership in bringing the Labour Party together from within the shadow cabinet. During the course of the meeting it became clear that this would not be possible," they said.

The resignations follow the loss of 12 members of Mr Corbyn's top team on Sunday, with Hilary Benn sacked as shadow foreign secretary and 11 others quitting in protest at his leadership.

Mr Corbyn responded by appointing loyal MPs to key positions in an effort to shore up his position but the second wave of departures from his frontbench team underlined the scale of the challenge he faces.

The Labour leader held crisis talks with Mr Watson in Westminster where he was left in no doubt that he would face a challenge to his position.

Mr Corbyn's office made clear that he would fight any contest - pointing out that he secured the position with a landslide win last year and claiming he continued to enjoy the support of the party's grassroots membership. He also received fresh indications of support from union chiefs.

The leader's office said Mr Corbyn would automatically be on the ballot in any leadership contest, meaning he would not have to find Labour MPs to nominate him.

Union leaders backed Mr Corbyn, with PCS general secretary Mark Serwotka saying he was "appalled" at the actions of the party's MPs.

He said the party needed to unite in its response to the European Union referendum result.

In a message to Mr Corbyn he said: "I am appalled that instead of helping with this, some self-indulgent Labour MPs are looking inward, and turning on you and the party members and supporters who elected you in a landslide last September.

"I believe you are the best person to lead the Labour party through what is undoubtedly going to be a difficult period and you have my full support."

Mick Whelan, general secretary of train drivers' union Aslef, said "Jeremy should be allowed to do the job we elected him to do until it is achieved".

Mr Corbyn filled the shadow cabinet seats vacated by the MPs who deserted him on Sunday with allies, including a number of MPs from the 2015 intake.

In one of the biggest moves, former shadow defence secretary Emily Thornberry will replace Mr Benn, who was sacked as shadow foreign secretary in the early hours of Sunday morning.

And Diane Abbott replaces Heidi Alexander, who quit as shadow health secretary - one of the 11 shadow cabinet ministers who resigned in protest. But as new jobs were allocated, the resignation letters kept arriving on Mr Corbyn's desk.