Ed Miliband attacked Alex Salmond's desire to "split up" Britain, 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."