Voting begins in the Labour leadership election today, as the publication of former prime minister Tony Blair's memoirs dominates the agenda.
Anyone joining the party before September 8 will be allowed to vote in the election, with the result announced on September 25 on the eve of the party's conference in Manchester.
The vote is an electoral college with the final result made up of individual ballots of MPs and MEPs, individual party members and affiliated organisations such as trade unions.
Voters will rank the candidates in order of preference from one to five. If one candidate secures over 50 per cent of the vote on the first round they are elected leader.
If no candidate secures over half the vote the contender placed last is eliminated and their second preferences are reallocated. Further rounds are carried out until someone makes it over the 50 per cent threshold.
In 1994, the last contested leadership race, Blair secured 57 per cent of the vote in the first round easily seeing off the challenge of John Prescott and Margaret Beckett.
And in what many will see as a coded endorsement of David Miliband over his brother Ed in their close fought fight for their party's top job, Blair has warned the party not to shift to the left.
Writing in his memoirs, published today, the former prime minister said: "The danger for Labour now is that we drift off, or even move decisively off, to the left.
"If we do, we will lose even bigger next time. We have to buck the historical trend and face up to the reasons for defeat squarely and honestly."
An hour long interview with Blair conducted by Andrew Marr to mark the publication of his book 'A Journey' will be broadcast on BBC 2 tonight at 7pm.
Seen as the frontrunner, David Miliband received a boost to his campaign today as the Daily Mirror swung its support behind his bid.
Under the headline "D-Day", the Labour supporting paper said they believed the shadow foreign secretary had the "intellect, talent and experience" to challenge the Conservatives and be Britain's next prime minister.
It said: "And we urge all those with a vote in the contest to rally behind him.
"Backing Mr Miliband has not been an easy decision. All five candidates have something to offer.
"But all Labour supporters agree on one thing: the party must reconnect with the people. The Mirror firmly believes David Miliband is the man to steer Labour to this recovery.
"His experience at the highest level of government is invaluable. He has a capacity to find new solutions to old questions. He is the one candidate the Tories fear."
While in a video posted on his campaign website Ed Miliband thanks his supporters and said the party needed to "change to win".
"This campaign is powered by people, powered by the thousands of volunteers who joined my campaign, to get back in to power to make our society more fairer more just and more equal," he said.
But outsider candidate Diane Abbott, the only woman in the race, has insisted the contest is still "wide open".
Writing on her campaign website she said: "Many people have asked me to state which of the other candidates I am backing as my second preference.
"They are all very good candidates, and would all make good leaders of the Party.
"But this contest is still wide open.
"Too many people have written this off as a two horse race. I think there will be some surprises when the results are announced at the end of the month."
Dods Parliamentary Communications Ltd