Ed Miliband attacked Alex Salmond's desire to "split up" Britain today, and insisted: "We are one United Kingdom."
The Labour leader attacked Scotland's First Minister over rising unemployment - which he said was the biggest challenge of all - but also on his links with media tycoon Rupert Murdoch.
He focused much of his fire in his speech to Labour's Scottish conference in Dundee on the Scottish National Party leader.
Mr Miliband insisted that "putting up a new border" between Scotland and England would not create a fairer society.
He said: "We must reject attempts to divide our country by ideology or geography. We are not left wing Scotland and right wing England, we are one United Kingdom."
He insisted that families, businesses and pensioners who were struggling in difficult economic times shared the same concerns, regardless of where they lived.
"People across the United Kingdom are united by wanting an economy that works for not just the few at the top but all the working people," Mr Miliband said.
"The small business struggling to get by in Stirling shares the same concerns as the small business struggling to get by in Southampton.
"And the pensioner in Dudley trying to keep warm shares the same concerns as the pensioner in Dundee."
He told the conference: "You should dream big dreams about the way you can change your country. Alex Salmond's vision is to break up Britain."
But he added: "My vision is different. It's to turn the irresponsible capitalism we have into responsible capitalism. It's to turn an economy that works only for the few at the top into one that works for every person in our United Kingdom.
"It's to turn the country that is betraying the hopes and dreams of young people into one that fulfils the promise of Britain and Scotland and sees the next generation doing better than the last."
The Labour leader had been delayed on his way to the conference, telling activists a fog-bound plane in London had made him late.
He conceded Labour had "lost badly" in last year's Holyrood elections which saw the SNP win an unprecedented overall majority in the Scottish Parliament.
With the Scottish Government now planning an independence referendum, he used his speech to argue against it.
While Mr Salmond argued in a speech in London that an independent Scotland could be a "progressive beacon" for the rest of the UK, the Labour leader insisted the SNP's "commitment to separatism" meant it could not be a "progressive force".
Mr Miliband said the First Minister had come to England to "brag" about that.
But he said: "Neither the politics they are practising in government or the separatism they would like to bring to the United Kingdom cannot answer the challenge of creating an economy that works for all the working people of Scotland and the United Kingdom.
"Only Labour can answer that challenge."
He highlighted rising unemployment in Scotland, saying the jobless total had risen faster over the last year than in England, adding that one in five young people north of the border are now out of work.
That "tragedy" he said has been caused by Westminster cuts and SNP "inaction".
Mr Miliband said both he and Scottish Labour leader Johann Lamont had gone into politics to "make Britain fairer".
But by contrast, he claimed: "Alex Salmond came into politics to change Britain's borders.
"SNP failure on youth unemployment didn't happen by chance, it happened by choice, the SNP's choice to make separatism the priority."
To help reduce unemployment, he pledged one of the first acts Labour would do if returned to power would be to insist companies who win major government contracts provide apprenticeships.
He also promised Labour would close a loophole that allows some train fares to rise by more than 1% above inflation.
Mr Miliband also said there should be action to ensure over-75s get the best deal on energy tariffs, saying: "The 350,000 pensioners over 75 here in Scotland, we must guarantee the lowest tariff available. And if the companies don't do it, the next Labour government will do it by law."
While he insisted Labour was standing up to vested interests, Mr Miliband hit out at Mr Salmond for his links with "the most powerful vested interest of all: Rupert Murdoch".
Mr Salmond met the News Corporation chairman in Edinburgh this week. The discussions came after the newspaper boss made comments on Twitter interpreted by some as showing support for Scottish independence.
His new The Sun on Sunday paper claimed to know the date of the planned referendum on independence: October 18 2014.
But Mr Miliband accused News International of having "sullied the character and reputation of British journalism".
He demanded: "What has Alex Salmond been saying about this? Has he been saying News International must clean up its act? Has he been saying they must behave far better and they must get to the bottom of wrongdoing? No. He has just been cultivating his relationship with Rupert Murdoch. His Twitter friend. His Sun on Sunday."
He told the First Minister: "If you want to be a progressive beacon it means speaking truth to power. Alex Salmond, you comprehensively failed that test on phone hacking and News International."
He added: "On jobs, the new economy, on vested interests, on living standards, on tax, the SNP aren't the progressive voice. And because of their commitment to separatism, they're not a progressive force either."
The Labour leader went on: "Putting up a new border across the A1 and M74: that's not going to help the man worried about his kids getting a job.
"New taxes to fund new embassies: that's not going to help the man needing a grant or a loan for his wind turbine business.
"And new passports to travel from Scotland to the rest of the United Kingdom is not going to help the poor pensioner either.
"The SNP answer: separation, division, isolation, putting up new borders; that's not going create an economy that works for working people."