Tony Blair has said he would not want a left-wing Labour party to win a general election.

The former prime minister said that even if he thought a left-wing programme was the route to victory, he would not adopt one.

“[Labour] misunderstand the difference between radical leftism, which is often in fact quite reactionary – and radical social democracy, which is all about ensuring that values are put to work in the most effective way,” he said.

“Let me make my position clear: 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.”

“Even if you did [win] it wouldn’t be right because it wouldn’t take the country forward, it would take it backwards. That’s why it’s not the right thing to do.”

Jeremy Corbyn speaks at the Durham Miners' Gala (Ian Forsyth/Getty Images)

Speaking at the Progress think-tank Mr Blair said anyone who supported Jeremy Corbyn “in their heart” needed to think about getting “a heart transplant”.

He further described the left-winger as “the Tory preference”.

The former leader said he would not positively endorse a candidate because it would “possibly not even [be] helpful for them”, however.

The first methodic poll of the Labour leadership campaign last night found that Mr Corbyn was on course to win the contest.

43 per cent of Labour supporters and members polled by YouGov for The Times newspaper said they would vote for Mr Corbyn in the first round of the contest.

Andy Burnham was in second place with 26 per cent, 20 per cent Yvette Cooper and 11 per cent Liz Kendall.

In the final round of voting Mr Corbyn would beat Mr Burnham by 53 per cent to 47 per cent.

Though polling such contests is difficult and the survey may not be an entirely accurate picture of the results, the figures do suggest that Mr Corbyn is doing very well.