Former Labour leader Ed Miliband has thrown his support behind Owen Smith, claiming the former shadow cabinet minister can unite his embattled party and "reach out to every part of Britain".
The Doncaster North MP, who resigned as leader of the opposition in the wake of the 2015 general election, added: "My choice in this leadership election is based on what our country needs at this extraordinary time after the European Union referendum. The decisions we make in the next months and years could define our country for decades to come.
"We've got a new Tory prime minister, Theresa May, who is claiming the language of the left but could take our country further right with a hard-Brexit plan.
"I want a Labour leader who can rise to the challenge of this moment, I want a Labour leader who can unite our party and make us a serious alternative government and I want a Labour leader who will reach out to every part of Britain and can do what Labour has done in the past, which is out of this crisis make it a progress moment. That's why my choice for Labour leader is Owen Smith."
The endorsement comes amid a war of words between Labour's deputy leader Tom Watson and Jeremy Corbyn's campaign, following a critical interview the West Bromwich MP gave to The Guardian newspaper.
Watson claimed Trotskyist entryists were seeking to undermine Labour by "twisting the arms" of younger members. But a spokesman for Jeremy for Labour hit back, accusing Watson of indulging in conspiracy theories and backing Smith's "Project Fear".
"Rather than patronising members and peddling baseless conspiracy theories about "Trotsky entryists", he should be working with Jeremy to unite our party so that we can get back to campaigning to dislodge this Tory government, and help elect a Labour government in its place," the spokesperson said.
The fiery exchange comes after a High Court gave Corbyn a boost yesterday (8 August) after it ruled new Labour members who joined after 12 January could have a say in the leadership contest without paying a £25 fee.
The decision could override Labour's National Executive Committee (NEC), but the party has vowed to appeal the decision at a hearing as early as Thursday (11 August). The latest opinion poll from YouGov for The Times, of more than 1,000 Labour members between 15 and 18 July, put Corbyn on 56% and Smith on 34% based on first preference votes.