Jeremy Corbyn has promoted key allies in an attempt to shore up his position as Labour leader but the revolt against him continued with further resignations and a threat by senior peers to boycott shadow cabinet meetings.

The Labour leader lost 12 members of his top team on Sunday and a series of junior frontbenchers quit on Monday as months of frustration at his leadership exploded into a full-blown coup attempt.

As Mr Corbyn moved to replace the members of the frontbench team who had quit, resignation letters continued to pile up on his desk.

The party’s leadership in the Lords appeared to back the effort to oust Mr Corbyn – who has vowed to fight on – although they will not resign their shadow cabinet seats.

Baroness Smith of Basildon, the Labour leader in the Lords, and Lord Bassam, the chief whip, are both in post because of elections within the ranks of the party’s peers rather than being appointed by Mr Corbyn.

A source said that they had taken “soundings” from the party’s peers and it was likely they would refuse to attend shadow cabinet meetings while Mr Corbyn remains as leader.

The embattled party leader appointed loyalist MPs into key roles in his shadow cabinet as he attempted to hold on to his position, including a number of MPs from the 2015 intake.

Former shadow defence secretary Emily Thornberry will replace Hilary 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 11 shadow cabinet ministers to resign in a day.

Other appointments confirmed by Mr Corbyn in his reshuffle were Pat Glass as shadow education secretary, Andy McDonald in the transport brief, Clive Lewis takes defence, Rebecca Long-Bailey will be shadow chief secretary and Kate Osamor is the new shadow development secretary.

The shadow environment, food and rural affairs portfolio has gone to Rachel Maskell, Cat Smith is the shadow voter engagement and youth affairs minister and Dave Anderson becomes shadow Northern Ireland secretary.

The chaos in the Labour ranks saw a string of junior frontbenchers follow the lead of their former shadow cabinet colleagues in quitting in protest at Mr Corbyn’s leadership.

Junior frontbenchers including Diana Johnson, Anna Turley, Steve Reed, Yvonne Fovargue and Toby Perkins resigned as the protest against Mr Corbyn’s leadership continued, with ministerial aides including Stephen Kinnock – the son of former Labour leader Lord Kinnock – also quitting.

A motion of no confidence is set to be considered at the Parliamentary Labour Party (PLP) meeting, with the possibility of a secret vote on Tuesday.

Former shadow education secretary Lucy Powell, who resigned on Sunday, insisted it was not a “planned coup” against Mr Corbyn, but instead a reaction to the “seismic” events which have shaken Westminster in recent days – the EU referendum result and David Cameron’s resignation.

Ms Powell was among 11 shadow cabinet members to resign on Sunday, while Hilary Benn was sacked from his post as shadow foreign secretary after months of frustration among Labour MPs over Mr Corbyn’s leadership.

Deputy leader Tom Watson, who expressed sadness at the resignations, is due to hold crisis talks with Mr Corbyn about the “way forward” for the party.

The meeting is seen as crucial because of the influence Mr Watson – who has his own mandate from the Labour membership – wields in the movement.

Ms Powell told BBC Radio 4’s Today: “I don’t know what Tom is going to discuss with Jeremy this morning, but I think it is now very clear that the position of Jeremy as the head of the Parliamentary Labour Party is pretty untenable and I hope that he would reflect on that.

“This is now a very difficult time for the country, we need strong leadership.”

She added: “I really do hope that Jeremy will now reflect on this himself and not drag this out any longer than necessary.”

In a tough talking statement on Sunday night, Mr Corbyn insisted he would fight for his job and contest any leadership challenge.

“I was elected by hundreds of thousands of Labour Party members and supporters with an overwhelming mandate for a different kind of politics,” he said.

Anyone who wanted to change the Labour leadership would have to stand in an election “in which I will be a candidate”, he vowed.

Asked if Mr Corbyn should resign, shadow chancellor John McDonnell told Sky News: “Not at all. He is the elected leader of the Labour Party, elected by the party members. They are the sovereign body. Jeremy shouldn’t resign at all.”

Mr McDonnell was asked whether deputy leader Tom Watson was offering full support to the leader. He said: “We will wait to see what Tom Watson has to say this morning. He’s meeting with Jeremy, but Jeremy will be appointing an alternative cabinet and they will be in place by lunchtime, so we will just continue on.

“If some members of the Parliamentary Labour Party want a leadership election, they can trigger that and there’ll be another leadership election and the members will decide. They are the sovereign body of the party.”