"I think it is absolutely imperative for Britain and the party that we win," she said in her interview with the New Statesman. "If we don't win it could be the end of Labour as a party of power at least for a generation, if not for ever. I have thought for the first time over the past few weeks that could throw away that victory."
She reserves special contempt for Tony Blair's coterie of unelected advisers, although she declined to name names: "I sometimes call them the people who live in the dark. Everything they do is in hiding. We go to the Shadow Cabinet, we go to the National Executive Committee. Everything we do is in the light. They live in the dark.
"These people are making a terrible error. They think that Labour is unelectable, so they want to get something else elected, even though really it's still the Labour Party. This is a dangerous game, which assumes people are stupid. It gets to the point where you are ashamed of your own past.
"They are saying: 'Vote for Tony Blair's New Labour. We all agree the old one was absolutely appalling and you all know that most of the people in Labour are really the old one but we've got some who are nothing to do with that, vote for us!' One, it's a lie. And two, it's dangerous. I think they're profoundly wrong."
She spoke of her anger and disappointment after her demotion in the last Shadow Cabinet reshuffle. "Since I was elected to the Shadow Cabinet last year I've experienced something I've never experienced before. You know that awful saying that in politics your enemies are behind you and your opponents in front of you, I thought it was one of those clever, cynical remarks. But I've had this experience of some people who meant to be on my side, one of whom I thought was a really good friend of mine, being dishonest and trying to hurt and damage me. It's very upsetting because if you don't expect it; it's shocking.
"I have seen this year some real nastiness, and I have felt some of it. And I hate it when people are all supposed to be on the same side, working on something as big, as important as this, and they're jockeying for themselves and they're lying about colleagues and they're trying to hurt people they're supposed to be working with."
Labour's front-bench team fared little better. "The Shadow Cabinet meetings don't bring out the best in people. We sit at a long thin table and there's no eye contact. It's all very 'boysy'. If anyone makes a silly joke, everyone laughs. It's also very patronage-driven. If you have one person in the room who controls everyone's fate it doesn't lead perhaps to the most honest discussion. The Shadow Cabinet away-days are better, but the political discussions are not of the quality of the NEC."
Without making a direct comparison with the former Labour leader, Ms Short finds Tony Blair lacking beside the late Labour leader, John Smith: "He [Smith] treated everyone with respect and you could feel it, people gelling and coming in. John was making the party feel more and more comfortable with itself. My own view is that he would have done that with the country. In the course of the leadership contest, after he died, all the candidates said they would continue with his inclusive style of leadership. I think we've lost it now."