Andy Burnham offers olive branch to Jeremy Corbyn

Mr Burnham will say in a speech in Manchester that it would be “unforgiveable” if infighting after the leadership result is announced on 12 September prevented Labour standing up to the Tories.

Ballot papers have been sent out to the first of more than 600,000 voters who can take part in the leadership election.

Mr Burnham is painting the contest as a race between himself and Mr Corbyn, and in doing so dismisses the chances of the two other candidates – Yvette Cooper and Liz Kendall.

Above: Andy Burnham questions Jeremy Corbyn’s credibility in an interview last month.

“Two candidates have put forward their visions and the party now must decide which way it wants to go,” he will say.

“I have put forward a plan that is both radical and credible, that can unite our party, that can speak to the country and lay the foundations for a Labour victory in 2020.”

And the shadow health secretary also sought to build bridges with Mr Corbyn, saying that he would involve the veteran left-winger in the “rebuilding” of the Labour Party if Mr Burnham is elected.

“Jeremy has brought energy to this race,” Mr Burnham will say. “I want to capture that and involve Jeremy and his team in rebuilding our party from the bottom up.

“I want to show how I can take the best ideas of the other candidates, where there is common ground between us, and use them to shape my radical vision.

“In that way, we will come out of this contest as a strong and united team ready to take the fight to the Tories.”

Above: Jeremy Corbyn on why the Labour Party should not become a Tory-lite

Mr Corbyn is the surprise frontrunner in the Labour leadership race, though has faced criticisms that his plans are not credible.

Former prime minister Gordon Brown warned at the weekend of the consequences of being a “party of protest” and said that Labour would be powerless to help the poorest of society unless it can win the next general election.

Meanwhile, Ms Cooper has insisted she is unaware of any attempt by Labour peer Lord Mandelson to suspend the election.

The Daily Telegraph reported that Lord Mandelson had encouraged Mr Burnham, Ms Cooper and Ms Kendall to quit en masse in order to suspend the Labour leadership vote.

Above: Liz Kendall tell Channel 4 News she will not back out of the leadership race

But speaking to the BBC, Ms Cooper said she was “not aware” if Mr Mandelson had contacted her office.

She said: “I’ve not discussed this with Peter Mandelson, I gather that there was some view that the process should be stopped because so many people were joining at the last minute.

“You need to pursue this with other people if people have told you things but my focus is on the leadership election that we have.”