Daily Mirror backs David Miliband in Labour leadership contest

David Miliband's Labour leadership bid was boosted today with support from the party's most vocal newspaper backer.

As voting in the contest began, The Daily Mirror used a headline of "D-Day" to proclaim the shadow foreign secretary as the best candidate to lead the party.

Ex-PM Tony Blair also used the publication of his memoirs to intervene in the election, with what is being seen as an attack on Mr Miliband's leadership rival and brother Ed, a former lieutenant of ousted premier Gordon Brown.

Mr Blair - who has accused Mr Brown of losing the election by abandoning New Labour - warned his party against a shift to the left, telling The Guardian: "If we take this path, the next defeat will be even more stinging."

He also said attacks on Tory cuts and Liberal Democrat collaboration might bring short-term benefit, but would stop the party from being an alternative government.

The Daily Mirror said its decision to back David Miliband had not been easy, describing his brother as the "big surprise" of the campaign.

But the paper underlined David's experience at the highest level of government, and said the Tories "really fear" him.

Yesterday Mr Miliband said he would be ready to serve in his brother Ed's shadow cabinet if he was defeated.

While younger brother Ed has made clear he would "definitely" serve under David, the former foreign secretary has so far been more evasive over the question of what he would do if he loses the race to succeed Mr Brown on September 25.

His move appeared to be an attempt to draw the sting from an escalating row between their respective supporters which threatened to recast the leadership contest as a divisive scrap between advocates of Old and New Labour.

As millions of ballot papers were sent out, David insisted that the election campaign had been "a warm comradely contest, a fraternal contest and... a contest that I think will bring credit to the Labour Party and will certainly not come in the way of our family."

Asked if he would serve under his brother's leadership, he told Five News: "Of course. You run in elections hopeful of winning but always secure in the knowledge that you might not win and that's life, but I think it's very important that now is a time for people to take responsibility for the party and the country."

Lord Mandelson, who has made little secret of his preference for David, sparked the clashes yesterday with a warning that the party would be stuck in an "electoral cul-de-sac" if it opted for a "pre-New Labour" agenda.

But Lord Kinnock - a supporter of Ed - hit back by accusing the former business secretary of being "sadly out-of-date" in suggesting there could be no deviation from the strategy which won Tony Blair three terms in office.

Leadership rival Ed Balls warned that the Miliband "soap opera" was in danger of drowning out debate over the party's future policy agenda.

And he insisted it "does not matter a jot" who Mr Blair backs in the leadership election and said his former mentor Mr Brown was "doing the right thing" in steering clear of comment on the contest.

Shadow health secretary Andy Burnham also denied the contest was a two-horse race, telling the BBC he was "in a strong third position and gaining ground" on his rivals.