Tony Blair has warned Jeremy Corbyn's Labour supporters to get a heart "transplant" or risk dragging the party back to the 1980s.
In a scathing intervention in the leadership race, the former Prime Minister urged party members to avoid "going back in time" to the electoral wilderness.
Speaking hours after a poll showed Mr Corbyn was on course to win the party’s leadership race, Mr Blair ridiculed those who said their “heart” wanted to back the leftwinger, declaring: “Get a transplant”.
He also said the Tory preference would be for Mr Corbyn to win, as they too recognised the historical electoral failures of far left parties in British politics.
Mr Corbyn responded by saying Mr Blair was making "silly remarks".
At a Progress event in London, the former Labour leader hit out at attempts to drag the party to the left, and said: “I wouldn’t want to win on an old fashioned leftist platform, even if I thought it was the route to victory, I wouldn’t take it.”
Mr Blair even suggested a Corbyn leadership would trap the party in a time warp, and said: “It's like going back to Star Trek or something. Back to the old days.”
He added: “2015 is not 2007 or 1997. So yes, move on. But don't for heaven's sake move back!”
@paulwaugh Blair had no heart at all for the people of #Iraq in 2003; nor a conscious since it seems
— Mags Donaldson (@mags0611) July 22, 2015
In the 75-minute event, the former Labour leader was scathing about the party’s direction under former leader Ed Miliband.
Mr Blair had remained relatively quiet in the past five years while Mr Miliband was leader, although before the election he did warn the campaign could be "a traditional left-wing party competes with a traditional right-wing party, with the traditional result".
Today, the former Labour leader frequently appeared exasperated as he questioned why Labour had moved away from the triple election winning politics of New Labour.
He added that since his three election victories the party had moved away from New Labour under Gordon Brown in 2010 and Ed Miliband in 2015 with predictable results.
Comparing the party’s current time in opposition with that of the 1980s, Mr Blair said: “We’re just going back in time.
"After the 1979 election the Labour Party persuaded itself of something absolutely extraordinary and when you think back on it it’s one of the most extraordinary things you can ever imagine…the Labour Party persuaded itself that the reason why the country had voted for Margaret Thatcher was because they wanted a really left wing Labour Party.
“This is what I call ‘The theory that the electorate is stupid’. Somehow they hadn’t noticed that Thatcher was somehow to the right of Jim Callaghan.”
Despite his criticism of Mr Corbyn, Mr Blair vowed that he would not quit if the Islington North MP won the contest and urged modernisers to stay and fight for their belief that the party could only win if it offered policies that reflected traditional values for the modern world.
Asked how he'd respond if the party voted for Mr Corbyn he replied: "If it does, I'm Labour through and through. Anyone who fought the 1983 campaign for the Labour party is Labour through and through."
Yet in a signal the party could face some of its bitterest infighting for decades, he said that staying in the party would not mean going quiet. He said: "'Unity' does not work if you're all together in the bus going over the edge of the cliff.
"The great unity thing...unity doesn't really work if you have a whole set of different positions and say just hold hands and pretend we agree".
He added: "Even after this leadership election there's going to be a debate in the Labour party."
With the YouGov/Times poll today putting Tom Watson way ahead of Stella Creasy for the deputy leadership, Mr Blair also had a dig at the MP who helped hasten his departure.
He said that he wanted to "get us away from machine type politics because it doesn't work" and “it could be important” to have a woman deputy.
While the Times/YouGov survey put Mr Corbyn on course to victory, a separate poll carried out by Anglia Ruskin’s Labour History Research Unit (LHRU) put Yvette Cooper out in front.
The survey of 294 Labour councillors across the UK showed Ms Cooper would take 52.1 per cent of the vote in a tight final run-off with Andy Burnham, who polled the highest score (30.95 per cent) in the opening round. Liz Kendall, who was named the candidate most feared by the Conservatives in a poll previously conducted by the LHRU in June, was eliminated in the first round with 13.95 per cent of the vote.
Mr Corbyn was eliminated in the second round of voting having polled 25.17 per cent in the first round, but saw his share of the initial vote rise by six per cent compared to the last LHRU poll in June.
Tom Watson is the preferred candidate for the party’s Deputy Leader, winning the final round of polling with 61.62 per cent in a head-to-head with Caroline Flint. Mr Watson was also the strongest supported candidate throughout, polling 42 per cent in the opening round.