Nominations for the Labour leadership contest have closed, with veteran left-winger Jeremy Corbyn securing the support needed for a place on the ballot.
Shadow health secretary Andy Burnham, shadow home secretary Yvette Cooper and shadow health minister Liz Kendall were already set for a place on the ballot paper, having each secured more than the minimum 35 formal endorsements from MPs.
A late surge for Mr Corbyn saw him reach the required number needed to secure his place in the contest, which will involve a series of public and televised hustings over the coming weeks.
His fellow Labour left-winger, John McDonnell, said: "As Jeremy's agent, I can confirm that he is on the Labour leadership ballot paper with 35 nominations. Thank you everyone."
As campaigning began in earnest, Ms Cooper used a highly personal speech to set out why she is the right person to rebuild the party after the general election defeat.
She said the leadership contest "needs to be about the future of the country not just the past of our party if we are to win again".
Speaking in central London, she said: "We have a long, hard road to support Scottish Labour rebuilding trust in Scotland. A task to win back the trust of Labour voters who switched to Ukip, angry with us and at the world and a vital challenge to persuade people who voted Conservative to come over to Labour - those who are worried about the economy or the future, especially in towns and suburbs across England and Wales.
"To win back the people who leant their support to David Cameron because they thought he was preferable to what Labour offered."
She added: "We won't deliver a Labour government by swallowing the Tory manifesto, Tory plans or Tory myths. In the end the Tories don't have the right values or the right answers for our country.
"Nor will we win by simply trying to splice together a shopping list of retail policies, targeted at different slices of the electorate. No 'vote Labour and win microwave'."
Setting out her own background as a "comprehensive girl" who secured a place at Oxford University, she said: "Born in Scotland, brought up in England, we moved around when I was young.
"My family are from the coalfield communities and industrial towns of the North, like the Yorkshire constituency I now represent.
"But I grew up mainly in Alton, a small town in Hampshire, a comprehensive girl and my first job was about as rural as it gets - picking fruit for £2 an hour on the local farm and learning to drive a tractor too."
Ms Cooper, who is married to former shadow chancellor Ed Balls, said Labour had to show voters they understood the big issues of the time such as the rise of nationalism, uncertainty over Europe, the threat posed by Islamic State and the "real challenges" in the economy.
She said: "In the 2015 election, I don't believe most people felt any party was facing up to those future challenges, or showing how we can earn prosperity and security in that changing world.
"Labour couldn't reassure those who felt threatened by change, nor could we convince those who wanted to be optimistic for their children that we had a credible enough plan for the jobs and opportunities they wanted."
Setting out a commitment to spend 3% of GDP on science, technology and innovation, she said: "We need to encourage the start-ups. Invest in science, technology and innovation.
"Make investment available to the entrepreneurs who are willing to take a risk. And make sure everyone has the chance to get into new and hi-tech jobs. But right now we're stalling."
While Germany, Scandinavian countries, Korea and Japan were spending 3% on science and technology "Britain is being left too far behind".
She added: "That's not good enough. We should set our ambition to increase our collective investment in our hi-tech future to 3% too. Using Government support to set incentives to boost private sector, universities and charitable investment in science and technology too."