Labour leadership: Andy Burnham makes unity bid as Labour supporters vote in election

Andy Burnham is set to bill himself as the "unity" candidate in the Labour leadership contest and reiterate his claim that he is the only hopeful who can beat left-winger Jeremy Corbyn. The former health secretary will make the plea as the first votes in the leadership race are expected to be cast after Labour sent out ballot papers on 14 August.

Burnham, the MP for Leigh since 2001, will argue that he has put forward a "radical and credible" plan that can unite his party, the Press Association reported. The 45-year-old will say: "The race has shown that the Labour Party is crying out for a big vision it can get behind. We can't carry on as we are and the good news is that this leadership election could bring real change to our party

"Two candidates have put forward their visions and the party now must decide which way it wants to go. 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."

Burnham will make the speech at the People's History Museum in Manchester, a North West centre for working-class culture. The address will come a day after the 196th anniversary of the Peterloo Massacre, a significant commemoration for those on the left. The grizzly 1816 day saw 15 protestors and hundreds of people injured after a group of local grandees and business owners led a cavalry charge into political reform campaigners in Manchester.

Burnham's address will also follow Gordon Brown's major intervention in the Labour leadership contest. The former prime minister had rarely been seen on the public stage since the general election, but the Scotsman spoke at the Southbank Centre in London to warn that Labour must be "credible" and "electable" to make a positive difference in people's lives.

"The best way of realising our high ideals is to show that we have an alternative in government that is credible, that is radical, and is electable – is neither a pale imitation of what the Tories offer nor is it the route to being a party of permanent protest, rather than a party of government," he said.

The speech came after other grandees, like Tony Blair and Alan Johnson, warned Labour supporters that a Corbyn victory on 12 September could damage the party. But the socialist firebrand remains the frontrunner in the race after a revised YouGov poll, which surveyed more than 1,000 supporters and was commissioned by The Times, put Corbyn 37 points ahead of Burnham (57% vs 20%), with Yvette Cooper on 16% and Liz Kendall on 7%.

Labour have revealed that more than 610,000 people have registered to vote in the contest, including 189,703 affiliated supporters, 121,295 registered supporters and 299,755 members. But the election has been surrounded by controversy after claims of left and right-wing entryism emerged around Labour's £3 "supporters" offer. However, the party has maintained that it has rigorous vetting procedures to stop political rivals from undermining the credibility of the contest.