David Miliband has made a last-ditch intervention in the Labour leadership contest and called on his party's supporters not to vote for Jeremy Corbyn. The former foreign secretary attacked the left-winger for apparently espousing anti-austerity policies reminiscent of Greek socialist party Syriza.

"Britain is not Greece. Neither in terms of our deficits and debts, contrary to the government's claims about its inheritance from the last Labour government; nor in terms of the political choices we face today, contrary to Jeremy Corbyn's demand that Labour become an anti-austerity movement on the Greek model," Miliband said.

The 50-year-old, who has become increasingly more vocal after his brother Ed led Labour to defeat at the general election, said the alternative to Corbyn is "passionate reform, not angry defiance" and the former frontbencher blasted the left-wing's programme for "looking backwards".

Miliband, who stood down from parliament in 2013 to head the charity International Rescue Committee in New York, also wrote in The Guardian that he would select Liz Kendall as his first preference in the election and Yvette Cooper as his second choice.

"The leadership election is about the country and not just the Labour party. It is in the interplay of the values, instincts and ideas articulated by Kendall and her supporters in her campaign, and in Cooper's speech, that Labour will ever return to government and improve the country. That is why I shall be casting my first and second preferences for them this week," he said.

The comments come after Gordon Brown, a former Labour prime minister, cryptically attacked Corbyn over the weekend during a speech in London and Tony Blair, one of the party's most successful leaders, called on the Islington North MP's supporters to "get a heart transplant". Corbyn has pushed the grandees into action after numerous opinion polls have put him in first place and set to win the contest.

The latest survey, conducted by YouGov and commissioned by The Times, found that the veteran parliamentarian was 37 points ahead of Andy Burnham (57% vs 20%, respectively), with Cooper on 16% and Kendall on just 7% based on first-preference votes.

Labour sent out its ballot papers to supporters on 14 August and people are expected to receive them today. The party has said more than 610,000 have registered to vote in the election, including 189,703 affiliated supporters, 121,295 registered supporters and 299,755 members.

Elsewhere, former business secretary Peter Mandelson was accused of "plotting" to discredit the election in a bid to stop Corbyn. The Daily Telegraph claimed the Labour peer had approached Burnham, Cooper and Kendall in an attempt to get the candidates to stand down in protest. But Cooper has denied that Mandelson, an architect of New Labour, talked to her about the plan.