The intervention comes as those vying to replace Mr Corbyn prepare to announce their leadership bids in the new year, with the contest formally expected to begin when parliament resumes after the Christmas recess.
In a letter, published in The Observer, the 11-strong group of defeated Labour candidates and MPs calls for an “unflinching” review into exactly what led to the party’s worst election result in terms of parliamentary seats won since 1935.
The party must, they add, go “way beyond a simple review”, in what appears to be a swipe at the proposed post-mortem involving a panel of senior Labour figures, including former leader Ed Miliband.
“We need to be honest about why our outgoing leadership’s reflexive anti-western worldview was so unpopular and address the reasons,” they urge.
The group of defeated candidates includes former MPs Mary Creagh, Emma Reynolds, Anna Turley, Dr Paul Williams, Gerard Killen, Martin Whitfield and Phil Wilson, who lost his Sedgefield seat formerly held by Tony Blair.
In a scathing assessment of Mr Corbyn’s leadership, they claim “cronyism” at the top of the party and a “repeated unwillingness to stand up to the stain of antisemitism” were relayed back to them on the doorstep during the general election campaign.
“The challenge for the eventual winner is immense,” they wrote. “We need to win 150 seats in every corner of the country, gaining votes from a coalition of communities.
“Labour needs to be in government – and for that, fundamental change at the top of our party is required. Only this will help us recover from the catastrophic loss of 12 December.”
They continued: “We were rejected on doorsteps not just because of our woolly, changing position on Brexit, or in Scotland because of our weak commitment to the union, but because the very people we were supposed to be fighting for did not think the policies in our manifesto related to their lives.
“The focus on nationalisation and uncontrolled spending commitments meant people simply didn’t believe us. Sadly, this was particularly true with those most affected by the poverty and injustice that 10 years of Tory government has created.”
Both shadow foreign secretary Emily Thornberry and Clive Lewis, a shadow treasury minister, have announced their decision to run. Others including Sir Keir Starmer, Lisa Nandy and Rebecca Long Bailey are all expected to enter the contest.
The letter from defeated candidates also comes as Jonathan Goldstein, chair of the Jewish Leadership Council, wrote in The Sunday Times that the election result was a relief for the “vast majority of of Jews in the UK”.
He added: “So what now for the Labour Party and the Jewish community? We hope for a new relationship but we are under no illusions. The problem is not Corbyn but Corbynism and Corbynites remain strong in the party.”
And in a warning to the new leader of the party, Mr Goldstein wriote “we will look for tangible signs that the new team wants to lead a genuine anti-racist party” and includes five suggestions.
They include apologising for the “whitewash” report into antisemitism by Baroness Chakrabarti, and making an effort to address a lack of confidence in the complaints procedure by implementing an independent process.