Tony Blair, the Labour Party's most successful election winner, told his party on Wednesday it could not win power in Britain by lurching to the left, urging it to embrace the centre-ground of politics instead.
Labour tacked to the left under Ed Miliband, who quit in May after leading the party to its worst election defeat since 1987. Now, in the midst of a period of soul searching as it picks his successor, the party is split over its future direction.
"You win from the centre, you win when you appeal to a broad cross section of the public, you win when you support business as well as unions, you don't win from a traditional leftist platform," former prime minister Blair said in a speech in London.
Blair won three elections in a row from 1997 to 2007 on a centrist "New Labour" platform.
He spoke as a YouGov poll published on Wednesday showed left-wing candidate Jeremy Corbyn, who had previously been regarded as an outsider, could become the party's next leader.
The poll of 1,054 people eligible to vote in the contest showed support for Corbyn at 43 percent, with the party's health spokesman Andy Burnham on 26 percent and its home affairs spokeswoman Yvette Cooper on 20 percent. Liz Kendall, considered the Blairite candidate, was on 11 percent.
"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," said Blair.
"Move on, but don't for heaven's sake move back. If we do then the public won't vote for us ... because our thoughts are out of touch with the world they live in today."
Blair said support for the radical left was "reactionary", and that Prime Minister David Cameron's Conservative Party wanted Corbyn, 66, to win because he would be easier to defeat.
He said he would not be endorsing a particular candidate for the leadership. But he added that those who said their heart was with Corbyn should "get a transplant".
"The modern world means that you have to change with it and if you don't, you get left behind," Blair said. "To articulate this idea of a modernising Labour Party is not a betrayal of your principles, it is actually the only way that you implement principles in the real world."
Corbyn, speaking to reporters in central London, rejected Blair's criticism and said Labour had not lost the election for being too left-wing, but for offering "austerity-light".
Blair also said Labour, which was almost wiped out in Scotland by the Scottish Nationalist Party (SNP) and lost many votes in the north of England to the anti-EU UK Independence Party (UKIP), needed to tackle the issue of nationalism head on.
"The SNP and UKIP have clouded our sense of direction because they seem to point away from the centre," he said.