Two candidates in the Labour leadership election have warned members they risk consigning the party to years in opposition if they choose left-winger Jeremy Corbyn as successor to Ed Miliband.
The warnings from Yvette Cooper and Andy Burnham came after reports of a private poll giving Mr Corbyn a lead of more than 20 points.
Bookmakers William Hill made the veteran backbencher favourite for the first time, slashing his odds to just 11/8, after posting him as 200/1 rank outsider when he first entered the race.
Ms Cooper told members it was time to "get serious", telling The Independent Labour would be "condemning our world to a Tory future" if Mr Corbyn wins.
And Andy Burnham said the party faces a "big choice" over "whether it is going to get straight back on a path towards government and getting a Labour government back or whether we are going to be a party of protest".
Mr Burnham told the BBC that a private poll seen by the Daily Mirror should be taken "with a large, large pinch of salt". The survey put Mr Corbyn on 42%, with Ms Cooper on 22.6%, Mr Burnham on 20% and Liz Kendall on 14%. In a final round run-off, Corbyn would edge the contest by 51% to 49% over Cooper, the poll suggested.
A spokesman for Ms Kendall dismissed the findings, saying: "A poll is something done by a recognised company with data published for all to see. This isn't a poll, it's just spin, and rather desperate stuff at that."
Mr Burnham acknowledged that Mr Corbyn's anti-austerity message was "striking a chord with people" but said that making him leader would be "the wrong choice".
The shadow health secretary said it was good for Labour to "think big again and dare to dream", but warned that Mr Corbyn must show how he would fund policies like free university education or renationalisation of utilities.
"Economic credibility has to be at the heart of everything we do," said Mr Burnham. "That's the first test you've got to pass if you want to be the next Government."
Ms Cooper said the surge in support for Mr Corbyn was driven by "frustration and anger" at the prospect of five more years of Conservative government.
But she warned that Labour must not "go back to the 1980s and just be a protest movement".
"I want Labour to be able to change the world once again," she said. "But we can only change it if we win. If we make the wrong choice in this election, we will be condemning our world to a Tory future."
Meanwhile, shadow business secretary Chuka Umunna said Labour should take its inspiration from the Partito Democratico of Italy's centrist Prime Minister Matteo Renzi, rather than Greek PM Alexis Tsipras's far-left Syriza, which has been praised by Mr Corbyn.
Speaking during a visit to Rome, Mr Umunna - who was tipped as a future leader from Labour's Blairite wing but withdrew from the contest shortly after throwing his hat into the ring - said Syriza had offered "fantasy" politics and "failed in its mission".
Mr Tsipras's approach was "fruitlessly prolonging the suffering of ordinary people", while Mr Renzi had cut taxes for the low-paid, increased exports and reduced unemployment by "combining economic competence with social justice", said Mr Umunna.
Mr Renzi's success should teach Labour that "legitimising the state means constantly improving its performance; to be truly radical is to effect substantial change, improving the lives of ordinary people; there is nothing right-wing about the careful use of public money, nor anything inherently left-wing about the politics of grievance," said Mr Umunna.