Deep divisions over economic policy have opened up in the Labour leadership race amid claims Jeremy Corbyn's plans would be a "disaster".
Shadow chancellor Chris Leslie claimed the veteran left-winger's strategy would push up inflation and interest rates, hitting the poorest hardest.
Mr Leslie, who said he would not serve in a shadow cabinet under Mr Corbyn, urged party members to "think carefully" about the impact of the Islington North MP's policies.
Meanwhile, Labour MP John Woodcock, who is backing Liz Kendall, said he is concerned about the party's image "taking a massive leap back to the politics of Michael Foot and the 1980s" following the surge in support for Mr Corbyn.
Mr Leslie told The Independent Mr Corbyn's plans to fund infrastructure investment by printing money would "push up inflation, lending rates, squeeze out money for schools and hospitals and mean spending more on debt servicing", with the worst impact hitting those unable to pay privately for services.
Mr Corbyn would be unable to eliminate the deficit through tackling tax avoidance and cutting tax reliefs, leading to further cutbacks in public services, with the result that "taxpayers will lose faith in the public realm, will become more sceptical and cynical, and be more likely to exit and go to private health and private education", he predicted.
Mr Leslie confirmed that "on principle" he did not think he would be able to serve in a shadow cabinet under Mr Corbyn, claiming a victory for the left winger would leave it a "very different" party from the one he joined.
Mr Leslie told BBC Radio 4's Today programme: "It would be a very different political party. It would not be the party I joined, but I would fight and stay to make sure we advocated thoughtfully why a centre-left agenda is the right way forward.
"Economic credibility isn't just about winning at all costs. There are reasons for caring about it, attending to those issues, rather than adopting ill thought through policies that, in the end, will hurt those on the lowest incomes, because those cost of living questions matter a massive amount.
"We need a credible Labour prime minister and this is why party members have got to think carefully because so much is at stake here."
Mr Woodcock claimed Mr Corbyn's policy would be a "catastrophic way" to deal with the country's problems and praised Mr Leslie for warning that printing more money would be a "recipe for economic disaster".
Mr Woodcock told BBC Radio 4's World at One: "It's not simply about political economic credibility - though that is of course of huge importance for the Labour Party - it's also that these things would not achieve their intended aim and therefore would end up hurting the very people the Labour Party was formed to represent."
Labour stalwart David Winnick said concern about the prospect of a victory for Mr Corbyn was not confined to the party's right wing.
Mr Winnick, who defined himself as being on the "broad left" of Labour, said: "It's simply not the case that it is only the right, the Blairites or those close to the Blairites, who are concerned about Jeremy winning."
Labour's decisive successes under Harold Wilson and Tony Blair had relied on winning a broad coalition of support, including persuading many Tory supporters to change allegiance for the first time, he said.
"There will be no decisive victory - and perhaps no victory at all - next time round unless we have a very broad front, unless the party is able to appeal to people outside the comfort zone," Mr Winnick said.
"I have much fear and anxiety that Jeremy will not appeal to the large section of the nation that we need to win over."
But he acknowledged that if Mr Corbyn did win "that must be totally accepted" and there could not be a move within the Parliamentary Labour Party to oust him.
Allies of Mr Corbyn rallied to defend "Corbynomics" - the left-winger's economic plans.
Richard Murphy, an economic adviser to Mr Corbyn's campaign and of Tax Research UK, said Mr Leslie has "got this completely wrong" as he defended the plan for "people's quantitative easing".
He told BBC Radio 4's World at One: "The real question for Chris Leslie is 'why did you support £375 billion for the banks?' when actually very much less would create jobs in every constituency throughout the UK, which is precisely what Jeremy Corbyn is offering by adopting this programme."
Richard Burgon, Labour MP for Leeds East who nominated Mr Corbyn, told the same programme: "Nobody wants to see Labour in opposition... but I do think it's unfair to characterise Jeremy Corbyn and his campaign as some sort of time travel back to the 1980s.
"If there's any travelling back in time going on it's the travelling back in time to the stale, out-dated Blairite 1990s. And what perhaps did work electorally in the 1990s wouldn't necessarily work now."