Yvette Cooper has claimed that she is the real radical choice in Labour's leadership election, not left-winger front runner Jeremy Corbyn. Cooper, a former work and pensions secretary, said the prospect of Labour electing its first female leader and running to become the next prime minister of the UK in 2020 trumps Corbyn's socialist policies.

The leadership hopeful made the remarks during a speech in Manchester today (13 August) after a YouGov poll put Corbyn 32 points ahead of Andy Burnham (52% vs 21%), Cooper on 21% and Liz Kendall on 18% on first preference votes.

"What is more radical? A Labour party after a century of championing equality and diversity which turns the clock back to be led again by a leader and deputy leader, both white men. Or to smash our own glass ceiling to get Labour's first elected woman leader and woman prime minister too. Who's the real radical? Jeremy or me?" Cooper said.

The former minister also argued that she offered a radical and "credible" alternative to the 66-year-old Islington North MP. Cooper added: "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."

Tony Blair, one of Labour's most successful leaders, has also made another intervention in the leadership contest. The former prime minister, writing in The Guardian, said: "If Jeremy Corbyn becomes leader it won't be a defeat like 1983 or 2015 at the next election. It will mean rout, possibly annihilation."

Labour last night released the final figures of the number of people who can vote in the leadership race. More than 610,000 people have a say in the contest, including 189,703 affiliated members (mainly union members), 121,295 (who have signed up as £3 "supporters") and 299,755 Labour members.

The election rules have been criticised by Labour grandees, including former foreign secretary Jack Straw. But party officials have said they have a rigorous checks and balance system in place, which has been able to weed out suspected entryists from rival parties. Notably, Toby Young, the right-wing columnist and Miranda Green, a former Liberal Democrat press secretary, have been caught out.

Ed Miliband's successor will be announced at a special party conference on 12 September after the leadership ballot closes on 10 September. The first ballot papers will be sent out tomorrow (14 August).