Labour leadership candidates
YouGov estimates that socialist firebrand Jeremy Corbyn is still set to win the contestGetty

It is the beginning of the end of the Labour leadership race as the party sends out its ballot papers today (14 August). The four hopefuls have been hitting the campaign trail and airwaves in a bid to secure votes but it could all be in vain as Jeremy Corbyn is still set to win the contest.

The socialist firebrand, a rebellious voice on the backbenches until recently, has a 37-point lead in the opinion polls based on first-preference votes. The figure comes after YouGov revised its most recent survey, which was commissioned by The Times and questioned more than 1,000 Labour supporters, to show the Islington North MP was set to secure 57% of the vote, against Andy Burnham's 20%.

The firm made the move after Labour revealed on Wednesday night (12 August) that more than 610,000 people had registered to vote in the leadership election, including 189,703 affiliate members, 121,295 "supporters" and 299,755 members. The prospect of Corbyn securing victory on 12 September, when Ed Miliband's successor is announced, has pushed his rivals into last-minute action.

Yvette Cooper, giving a speech in Manchester yesterday (13 August), claimed she was the real "radical alternative" in the race and the former work and pensions secretary argued she also offered economic credibility.

"The radical approach of the future is to reform capitalism so it serves people, not to try to destroy it with nothing to put in its place. To reform markets so power isn't concentrated, so they encourage the talents and ideas of all, invest in the long term, not return to clause IV as Jeremy has suggested," she said.

Liz Kendall, seen as the "Blairite" candidate in the contest, warned on 14 August that Labour would sign a "resignation letter to the British people as a serious party of government" if its supporters elected Corbyn. She also told BBC 4's Today Programme: "His programme isn't new, it's exactly the same as it was in the 1980s and we'll get the same result."

However, Kendall is unlikely to win the contest. The shadow care minister has consistently trailed in the opinion polls and YouGov's revised figures put her on just 7%. But the 44-year-old, who has secured the big-name backing of Chuka Umunna and Tristram Hunt, has refused to quit the contest.

Burnham, once seen as the bookies' favourite, has also attacked Corbyn by questioning the socialist's economic credibility. The former health secretary told the BBC on 14 August: "Jeremy's plan lacks credibility. It's not possible to promise free university education and renationalising the utilities without that coming at a great cost. If you can't explain how that's going to be paid for, then I don't think we will win back the trust of the voters on the economy."

The comments come after Burnham, the MP for Leigh, criticised Cooper for attacking Corbyn. Burnham's campaign was boosted this morning (14 August) when The Daily Mirror threw its support behind him, while The Guardian has come out for Cooper. Elsewhere, Corbyn will address his supporters at a rally in Edinburgh later today.