Prime Minister Tony Blair has warned of the cost of Scottish independence, a week before the Holyrood election.
Tony Blair said independence was more than a theory
At the same time, Scots Tory leader Annabel Goldie made a passionate defence of the Union.
In a hard-hitting speech, she said Labour's Jack McConnell and Lib Dem Nicol Stephen were as much a threat to the UK as SNP leader Alex Salmond.
The SNP said it had "no doubt" that Scotland would benefit from increasing success under independence.
Mr Blair claimed the SNP's economic policies were beginning to unravel, just days before voters went to the polls.
Speaking at Neilston, East Renfrewshire, with First Minister Jack McConnell, the Prime Minister claimed multi-earner households would lose out through Nationalist plans to replace the council tax with a local income tax.
He said the SNP had miscalculated how much oil revenues an independent Scotland could expect and that their independence referendum was a recipe for "conflict and instability" from the first day of an SNP administration.
Mr Blair defended the Union, but warned that the issue of independence went wider than dry constitutional theory.
"It's not just about the constitution as if it was some sort of academic theoretical question," he said.
"It's about hard issues that effect the lives of real people."
Mr Blair also praised Scottish Labour leader Mr McConnell, stating: "The one thing I know about Jack McConnell is that when Jack gets up each morning what is on his mind is education.
"When Mr Salmond gets up each morning what is on his mind is separation."
In a "state of the Union" address in Edinburgh, Ms Goldie said the previous Lib Dem and Labour coalition had failed Scotland.
She also stressed the advantages to Scotland of being in the Union including membership of the G8, Nato and the UN Security Council.
"As part of the United Kingdom Scotland shapes the world, outside the United Kingdom the world would shape Scotland," she said.
"The Union opened doors for Scotland. Why on earth would we want to slam them shut?"
A clear majority of unionist parties would be returned in next Thursday's vote, she added, but claimed that SNP leader Alex Salmond was not alone the biggest threat to the Union.
"Two other men pose an equally serious threat - these men are Jack McConnell and Nicol Stephen," she said.
"Their incompetence in running the country has made Scotland question devolution."
Annabel Goldie said the Union had opened doors for Scotland
An SNP spokesman said a Nationalist government would be all about success for families across Scotland.
"From day one we will be focusing on new opportunities for Scots and putting in place the important improvements so our communities can be safer, our nation healthier and families wealthier with fairer and lower local tax," said the spokesman.
"It's time for a government that cares about Scottish success and creates the conditions for Scots and Scotland to flourish."
In response to Ms Goldie's attack, on Mr Stephen, the Scottish Lib Dem leader, his party's election director Tavish Scott said the Tories were irrelevant in Scotland.
He said: "Annabel Goldie's comments simply underline the desperate straits the Tories are in.
"People in Scotland won't forget the Tory's poll tax, or that crime went up by 168% under their rule.
"They have already consigned their manifesto to the dustbin, promising not to implement a single one of their policies."
Mr Scott added: "It's this type of negative, personal attack that turns people away from the Tories and why more and more people are moving to the Liberal Democrats."