Jeremy Corbyn is facing a fresh backlash from MPs, triggered by his controversial shadow cabinet reshuffle.
Labour began a new round of bitter in-fighting as the chairman of the parliamentary party strongly criticised the timing of the top level shake-up.
John Cryer issued an angry letter to MPs saying he and sacked chief whip Rosie Winterton had been kept in the dark about the major transformation of Labour's front bench, despite being engaged in crunch talks with the leadership on having some of the places on the body put up for election.
"We held a number of meetings, most recently during Labour conference, and were genuinely hopeful that we could get to an agreement which would have the chance of drawing the PLP together so that we could go forward in a more unified manner than has hitherto been the case," he said.
"Rosie and I were keen to continue these negotiations this week and tried to arrange meetings with the leader's office to come to an agreement as soon as possible.
"However, it became clear on Wednesday that a reshuffle was under way, which had not been discussed or mentioned. It now seems to me that the party's leadership did not engage in the talks in any constructive way. Obviously, I deeply regret this turn of events."
A spokesman for Mr Corbyn hit back, saying he was ready to continue talks with the new chief whip.
"Shadow cabinet elections will be considered by Labour's national executive committee as part of a wider party democratisation at a special meeting next month," the spokesman said.
Critics attacked Mr Corbyn for engaging in a "revenge reshuffle" which saw the key posts go to his arch-loyalists.
Mr Corbyn completed his reshaping of Labour's front bench by appointing his deputy Tom Watson, with whom he has had a tension-filled relationship, as shadow culture secretary.
Mr Watson led failed negotiations to broker a peace deal between Mr Corbyn and the bulk of the parliamentary party opposed to him after the mass shadow cabinet walk-out in June.
The final line-up sees key Corbyn allies John McDonnell and Emily Thornberry retain their posts as shadow chancellor and shadow foreign secretary respectively.
This means that with Diane Abbott shadowing the home office brief, the three top posts are held by Corbyn loyalists - and London MPs.
There was said to be unhappiness among Labour MPs at the promotion of Mr Corbyn's long-time ally Ms Abbott to such an important post, and the sacking of chief whip Ms Winterton, seen as a key link with the backbenches.
Clive Lewis was moved from the defence portfolio to become shadow business secretary following the controversy which erupted at last week's Labour Party conference when the leader's office doctored the ex-soldier's speech on Trident at the last minute.
Jon Ashworth, one of the few remaining moderates in the shadow cabinet, was promoted to shadow health secretary, but has lost his place on the party's ruling National Executive Committee to a Corbyn loyalist, which could tip the finely balanced body in the leadership's favour.
Mr Corbyn responded to critics, saying: "I have acted to bring together a strong and diverse opposition leadership team."
In a surprise move, the Labour leader brought in Nick Brown, a long-standing ally of former prime minister Gordon Brown, to replace Ms Winterton as chief whip.
And Sir Keir Starmer, the former head of the Crown Prosecution Service who stormed out of his front-bench position as immigration minister, has been brought into the shadow cabinet as shadow Brexit secretary.
It brings forward a major moderate figure to the top team, in a signal that Mr Corbyn is prepared to allow some room for his critics.
Though only a handful of the 63 people who quit the shadow cabinet in the summer returned to the fold, more may take the remaining raft of junior posts yet to be announced.
The shadow minister for diverse communities, Dawn Butler, defended the appointment of MPs with low profiles.
"They might be obscure, but they are competent," she said of the new team.
Shami Chakrabarti, the former Liberty director who carried out a controversial investigation into anti-Semitism in the Labour Party, has been named the new shadow attorney general.
In a bid to stress regional balance in the top team, Mr Corbyn said the appointment of Jonathan Reynolds to the role of shadow economic secretary to the Treasury meant there were 10 MPs from the north of England on the front bench.