Yvette Cooper has launched a withering attack on the policies of Labour leadership rival Jeremy Corbyn, warning his economic policies lack "credibility" and the left-winger is offering "old solutions to old problems".
Against calls from moderates for Labour MPs to get behind one "Anyone But Corbyn" candidate, the Shadow Home Secretary unleashed a no-holds barred critique in a clear attempt to regain ground on the frontrunner.
More than 600,000 people have applied to take part in the leadership election, a three-fold increase in the party's membership since the election, buoyed by the £3 fee for "supporters" to join.
But with Tony Blair fearing "annihilation" if Mr Corbyn wins, Ms Cooper spoke in Manchester today of the "battle for the soul of our party" and how she would "not duck that fight"
In a key section of the speech, she says:
"I can see why many people have bought into what Jeremy is offering.
"I’m not going to dismiss the values and the intentions of Jeremy and those who are supporting him. I’m not going to claim they don’t believe in social justice or the ideals of the Labour party because I don’t think that’s right.
"But nor am I going to pander or pretend I agree with them on the answers, and claim I’m just a more electable version of what they stand for.
"Because the truth is that Jeremy is offering old solutions to old problems, not new answers to the problems of today.
"We have to look the 21st century in the eye, face up to the future
"That’s where we will find the new radicalism, the answers in the modern fight for social justice, equality and solidarity
"Not the old answers of the past."
She fears that Mr Corbyn, who stands on an anti-austerity, pro-nationalisation ticket that includes re-opening the coal mines, provides the "wrong answers for the future".
"They aren’t radical. And they aren’t credible. That they won’t change the world, they will keep us out of power and stop us changing the world," she said.
Ms Cooper goes in that aiming barbs at the "most popular candidate in the race may lose me votes". "But it needs to be said," she added.
"Our party, the values we stand for, and the country we want to fight for are too important not to be honest about what is at stake.
"And I want to show today that there is an alternative that is both radical and credible, true to our values, but serious enough to win. And we have to fight for it before it is too late."
Ms Cooper warned against Mr Corbyn flirting with a return to clause IV, Labour's commitment to shared ownership of major industries.
"People say they want radical politics," she said. "So tell me what you think is more radical.
"Bringing back clause IV: spending billions of pounds we haven’t got switching control of some power stations from a group of white middle aged men in an energy company to a group of white middle aged men in Whitehall.
"Or extending Sure Start; giving mothers the power and confidence to transform their own lives and transform their children’s lives for years to come.
"What is more radical? False promises to the South Wales mining communities you will re-open the now capped and flooded pits or investing in the green technology including clean coal technology of the future."
She adds Mr Corbyn's "radical alternative" for the economy, essentially printing money through quantitative easing to boost public investment, isn't "credible".
She said: "Printing money year after year to pay for things you can’t afford doesn’t work – and no good Keynesian would ever call for it."
And she warns being out of power, which a Corbyn leadership would presage, "won’t get us elected".
She said: "We can’t just luxuriate in our own righteousness out on the side lines. That’s not a luxury the most vulnerable in Britain can afford.
"It’s not enough to be angry at the world. We’re the labour party, we have a responsibility to change the world or what’s the point of us at all."