Senior allies of Jeremy Corbyn have unleashed a bitter attack on Sir Keir Starmer, claiming he should issue a "full-throated apology" for backing a second Brexit referendum at last December's general election.
Left-wingers Ian Lavery, party chairman under Mr Corbyn, and former shadow cabinet member Jon Trickett - both sacked by Sir Keir when he became leader - claim Labour's Brexit policy was an electoral disaster.
Their attack comes in a hard-hitting report on Labour's crushing election defeat, published on the eve of results of elections for the party's ruling national executive which have seen a left-right battle for control of the party.
Mr Corbyn's allies have mostly pulled their punches in their criticism of Sir Keir since he became leader in April.
But since Mr Corbyn's suspension over his antisemitism defiance last month, it appears the gloves are off.
"Labour got on the wrong side of the Brexit debate," the MPs claim in their report, "No Holding Back", co-written with defeated former MP Laura Smith following conversations with party activists and voters.
"People repeatedly claimed that Labour had become too southern and too middle class. We do not believe that Labour's problems in the so-called "red wall" areas began and ended with Brexit.
"Leave voters were too often sneered at and Remain voters were led up the garden path with a position - of overturning the referendum result - that was never seriously achievable.
"People who had supported Remain were sold a falsehood that not only could the result of the referendum be overturned, but that every version of Brexit was disastrous.
"This discourse was relentlessly pursued by senior politicians despite there never being a realistic prospect of it happening."
In a thinly veiled attack on Sir Keir, who was shadow Brexit secretary under Mr Corbyn and architect of the party's Brexit policy in the election campaign, the MPs argue: "Some should have known better.
"They were right at the centre of the Corbyn project and said that they were agnostic on the question of leave versus remain without ever setting out a credible position based on that. In the end though, they joined in the pressure to shift Labour into a remain position fully aware of the consequences."
And the left-wing trio are demanding: "A full-throated apology from Labour to the people for ignoring the democratic principle for which the labour movement has fought for centuries and for treating both sides of the debate with contempt.
"It is our contention that leading elements in the Labour Party moved us too far in one direction - away from our working class base and towards a more metropolitan middle class.
"In other words, away from communities that reliably voted Labour for generations, to a more mobile cohort who treat political support like choosing a branded product. It is a dangerous strategy."
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The MPs add: "We would like to offer some comradely advice to the new leader. Firstly, he should not bury under the carpet his role in Brexit. It will come back to bite him and Labour. Building trust is critical.
"Secondly, to win back working people, he needs to listen. Focus groups only tell you what you want to hear.
"If he did listen, he would hear some of the things that we have heard from working people as we have run the biggest listening project amongst members and trade unionists since the election across the country."
And in defence of Mr Corbyn, widely criticised as a turn-off to voters in the election, the MPs argue: "Some say that Jeremy Corbyn himself was an issue on the doorstep.
"It is true that Jeremy's leadership style was unique, and as such created an opportunity for media pundits to go for him repeatedly.
"The issue of media smear campaigns against Jeremy Corbyn came up a lot in our discussions.
"Issues around his perceived lack of patriotism, which focused mainly on failing to sing the national anthem, were central to these criticisms."
