A new group formed by Ed Miliband's former policy chief aimed at ensuring the party builds "a broad coalition of support" has been welcomed by Jeremy Corbyn.
Labour Together is being spearheaded by Jon Cruddas, who wrote a scathing analysis of the party's general election defeat which concluded that anti-austerity policies were a vote loser.
The MP nominated Mr Corbyn for the leadership to broaden the debate but warned during the contest he could turn the party into a 1980s revival "Trotskyist tribute act" and said his diagnosis was "at odds with where the country is".
He said the group - which also involves shadow energy secretary Lisa Nandy, MP Steve Reed and the leaders of Leeds and Newcastle councils - would "work with members who supported any of the four leadership candidates and with organisations across the spectrum of the Labour movement.
"The country needs a Labour party capable of boldness, but absolutely clear that what matters is building a broad coalition of electoral support. We didn't do that in 2010 and we ignored it in 2015," he wrote in The Guardian.
"So this week we launch an organisation called Labour Together. We will support grassroots Labour in our communities. We know that Labour only wins when it is united and when it is patriotic and speaks for the whole country.
"Jeremy Corbyn has rightly challenged the party to rethink the way in which it does politics. This is a challenge we wholeheartedly embrace."
The launch comes at a time of fears among some moderates that the Corbyn-aligned Momentum group will be a vehicle for a takeover of the party by the left, including deselections of MPs - a charge denied by its founders.
Mr Corbyn said: "I welcome Labour Together as a good initiative that explores a new kind of way to do politics. I am looking forward to working with them."