Scottish independence: Clegg and Miliband challenge SNP
The leaders of Labour and the Lib Dems have attacked independence in speeches to their Scottish party conferences.
Nick Clegg said the SNP must come clean on its plans, while Ed Miliband argued the move would undermine work to build a fair society.
The Liberal Democrats kicked off their spring conference in Inverness, while Labour is meeting in Dundee.
The Scottish government had said it wanted to hold a referendum on independence in the autumn of 2014.
In their keynote speeches, the Lib Dem and Labour leaders also set out their plans for boosting the economy.
What the leaders said on independence
Labour's Ed Miliband - "Alex Salmond [SNP leader] came into politics to change Britain's borders. It's not by chance that the SNP have failed the young people of Scotland it's their choice to make separatism the priority."
Lib Dem Nick Clegg - "What Scot doesn't have any English, Welsh or Northern Irish in their family tree? I believe the bonds that bring us together are stronger than the forces that would tear us apart."
On independence, Deputy Prime Minister and Lib Dem leader Mr Clegg said the nationalists still had many questions to answer on how an independent Scotland would work.
And he called for the referendum to be held "sooner, rather than later", with a single, clear question on the ballot asking whether people supported Scotland going it alone, rather than including a second one on more powers for Holyrood.
Labour leader Mr Miliband told members of the Scottish Labour Party faithful that people across the UK "owe obligations to each other", which would be thwarted by ending the union.
Creating a new border between Scotland and England, Mr Miliband said, would not enhance economic fairness.
Rather, the objective should be for the nations of the United Kingdom to work together.
He said that to every problem, the nationalists' answer was the same - separation, division and isolation.
The Labour politician said that throwing up a border across the A1 and M74 was going to help the SNP.
He added: "The way to beat the Tory-led government and the SNP government is not different, it's the same - to show how our values can make our country work for the working people of Britain."'Failed the young'
Mr Miliband said that he and Scottish leader Johann Lamont had come into politics to make Britain fairer.
But he added: "Alex Salmond [SNP leader] came into politics to change Britain's borders.
"It's not by chance that the SNP have failed the young people of Scotland it's their choice to make separatism the priority."
Once upon a time, it was Labour and the Liberal Democrats which were the main political force in Scotland.
They served for eight years in coalition government at Holyrood, but, the voters' desire for change has seen the SNP win more popular support at the polls than any other party since devolution in 1999.
Ahead of the independence referendum - likely to be held in autumn 2014 - Labour and the Lib Dems face the challenge of teaming up to make the case for the union.
At the same time though, they also have to rebuild their parties in the face of tough losses at the last Scottish election.
For Labour, it has to up its role as an effective main opposition party and government-in-waiting.
And the Lib Dems have to counteract their perceived unpopularity in Scotland, after doing a deal with the Tories at Westminster.
Before the referendum though, comes the council elections in May, which could well bring further electoral woes for the two parties.
Meanwhile, in his bid to make a case against independence, Mr Clegg said the people of the United Kingdom had a "rich, shared heritage".
He told his party's Inverness gathering: "We live side-by-side in towns and cities across the British Isles.
"Scottish, English, Welsh and Northern Irish people are together every day, in offices and factories, school classrooms and playing fields.
"We have rallied together in hard times, our forefathers fought together and died together, just as brave Scottish, English, Welsh and Northern Irish service men and women are fighting side-by-side in faraway lands right now."
Mr Clegg went on: "For centuries we have crossed each others borders, married each other, raised families together.
"What Scot doesn't have any English, Welsh or Northern Irish in their family tree?
"I believe the bonds that bring us together are stronger than the forces that would tear us apart."
The politician said he hoped that the people of Scotland would choose to stay in the UK.
He told conference that "as an Englishman" he believed that the UK was stronger with Scotland in it.
Mr Clegg added: "Scotland, like the other parts of the UK, has fared better in this global economic crisis than many of our European neighbours because we are part of one of the world's strongest economies.
"We have all been protected from the worst of the recession by the credibility and low interest rates the UK government has been able to secure and maintain."