Jeremy Corbyn has promised a "new kind of politics" if he wins the Labour leadership contest as the party prepared to send out the first ballot papers.
The left-winger, who has emerged as the surprise frontrunner to take control of the party on September 12, will continue his campaign in Scotland - where Labour suffered a catastrophic defeat in the general election.
The backbench MP's leadership rivals have clashed over how to halt his momentum, with Liz Kendall calling for voters to use their second and third preferences in an attempt to block Mr Corbyn, Andy Burnham urging a "positive campaign" and Yvette Cooper criticising the left-wing favourite.
Mr Corbyn will formally launch his 10-point "Standing to Deliver" plan in Glasgow, and will post a copy to all Labour Party members in the hope of securing their vote as the ballot papers start to arrive on doormats.
His policies include a commitment to "growth not austerity", nationalising the railways and energy sector, and a plan for nuclear disarmament.
Labour was almost wiped out in its Scottish heartlands in May, with just a single MP left after the SNP landslide, and Mr Corbyn said the party could not regain ground unless it fundamentally changed.
He said: "I have chosen Scotland to set out the values and policies I'm standing to deliver, on the day the ballot papers are sent out, because Scotland is one of several examples of how Labour has become disconnected.
"Labour cannot win in Scotland without change; and Labour cannot have a path back to power that fails to speak to Scotland.
"This plan of the values and ideas I'm standing to deliver are intended to speak to all parts of Britain, not setting one against another as the Tories have done.
"Combined, they are a new kind of politics: a fairer, kinder Britain based on innovation, decent jobs and decent public services."
Ms Kendall, in an interview with The Independent, urged supporters to use their second and third preferences to back Mr Burnham and Ms Cooper.
Under the Labour election rules, if no contender wins outright with more than 50% of first preferences, the bottom one drops out and the second preferences of their backers are reallocated to the other candidates.
With the polls indicating Ms Kendall could finish fourth, her supporters' choice of second preference could influence the result.
She said: "I will be using my second and third preferences ... It won't be for Jeremy.
"I will be strongly urging all of those who are putting me as their first preferences to use their second and third preferences."
Ms Kendall did not reveal who would be her second preference but added: "The main thing people need to consider is who is the best-placed person to win against Jeremy."
Mr Burnham received the support of the Daily Mirror in an editorial which said he is the leader who will "unite his party and deliver for the people who need Labour most".
But it urged Mr Burnham to "find a role for the man who lit up the election campaign, Jeremy Corbyn" in his team.
The newspaper recommended that voters should use their second preference to back Ms Cooper.
Ms Cooper's campaign received a boost as the Guardian endorsed her in an editorial which said that although Mr Corbyn had "breathed extraordinary life" into the campaign, he would not be able to win the votes from the Tories necessary to clinch victory at a general election.
Although Ms Cooper, like rivals Mr Burnham and Liz Kendall, had "failed to inspire" during the campaign, the newspaper concluded she was best-placed to take on David Cameron and would represent a historic first for Labour, which has never elected a female leader.
The first of more than 600,000 ballot papers will be sent out to long-standing members who have already been verified amid concerns about the way the contest is being conducted.
The new leadership rules have seen more than 120,000 people pay £3 to qualify for a vote - raising fears of political opponents undermining the process - and almost 190,000 from trade unions and other affiliates sign up.
Ms Cooper said a victory for Mr Corbyn could result in a split in the Labour Party and leave it out of power for a generation.
"I think there is a serious risk that the party will split, will polarise and I cannot bear to see that happen because there is too much at stake," she told BBC2's Newsnight.
She said the contest was a "battle not just for the soul of the party but it is a battle for all the people we should be standing up for".