ED Miliband has made victory in the independence referendum Labour's top priority in the final five months before polling day.
The Labour leader said the vote on September 18 was about "the fabric of the country".
The outcome, he said, was key to his goal of delivering a policy programme based on social justice from government after next year's UK General Election.
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Mr Miliband - whose chances in the election rely heavily on winning seats north of the Border - also insisted he was confident of defeating a Conservative party "in retreat".
Asked about the importance of the referendum in an interview with The Herald, he said: "This is well beyond an individual party's interests. This is about the fabric of the country.
"There is no bigger priority for Labour in the next few months because this is about the fabric of the country and we know how high the stakes are. We've got such common bonds that link us together across the UK.
"Because of bonds of emotion, because of how I believe we create social justice, I think it's an absolutely top priority."
Mr Miliband was speaking before a meeting of his Shadow Cabinet at the Emirates Arena, the new Commonwealth Games venue in the east end of Glasgow.
The visit to Scotland of the party's most senior MPs was part of a drive to build support for a No vote among traditional Labour voters who are undecided about independence.
The SNP have also targeted wavering Labour voters in recent weeks, with Deputy First Minister Nicola Sturgeon claiming independence would allow them to "reclaim" a party she said had lost its values.
Mr Miliband yesterday dismissed the Nationalists' overtures, insisting Labour plans to raise the top rate of tax to 50p, freeze energy bills and a new pledge to crack down on exploitative zero-hours contracts positioned his party as more progressive than the SNP and Alex Salmond's vision for an independent Scotland.
He said: "I believe the progressive choice, the social justice choice, the equality choice is for Scotland to stay within the UK."
Highlighting the SNP's plan to cut corporation tax, the main tax on business profits, by 3p, he insisted: "They can't match us. He added: "Let's look at the two prospectuses on social justice and I believe we will come out on top."
He accused the SNP of trying to "pump up" the prospects of a Conservative victory at the next election to boost support for a Yes vote, despite Labour's continuing lead in opinion polls.
He said: "This is a misreading of the Conservative Party's UK position. They haven't won a majority across the UK for 22 years.
"They haven't a single Conservative councillor in Manchester, Newcastle or Liverpool.
"This is party that has lost half its members under David Cameron. This is a party that is not advancing but is a party in retreat across the UK. "This is an absolutely beatable Tory Government. I feel confident about the next election, we've got a year to go and I believe we can be only one Christmas away from electing a Labour government."
He also backed the role played by the cross-party pro-UK Better Together campaign, whose head, Alistair Darling, has attracted criticism from Tory figures.
He said: "I think Alistair is doing an excellent job and Better Together is playing a really important role."
Mr Miliband backed handing more powers to Holyrood, saying devolution was "not a fixed point," and rejected SNP claims he was planning to scrap the Barnett formula, the funding mechanism that provides Scotland with higher public spending per head than the rest of the UK.
He was later joined by Scottish Labour leader Johann Lamont and Shadow Scottish Secretary Margaret Curran at a question-and-answer session in Motherwell.
Scottish First Minister Alex Salmond said the Labour leader had "zero credibility" on social justice. He said: "Labour has abandoned its principles and its leadership by working hand in glove with the Tories and the Westminster establishment against Scotland taking its future into its own hands."