ED Miliband has urged voters in Scotland not to "gamble" on the SNP as he insisted his opposition to doing a post-election deal with Nicola Sturgeon's party is because of principle.
The Labour leader declared his party could not "do a deal with a party that wants to break up the UK when we want to build it up".
He made the comments as he joined Scottish Labour leader Jim Murphy at a General Election rally in Glasgow.
With less than a week to go until polling day, Labour is facing heavy losses in Scotland, where support for the SNP has been surging since the independence referendum.
While this reduces Labour's chance of winning a majority at Westminster, Mr Miliband again made clear that he would not do a deal with the SNP after May 7.
He said: "I know the people of Scotland want a more just society. And with food banks, payday lenders and the neglect of the NHS, Scottish people feel there must be no delay.
"That's why I have a clear message for the people of Scotland today: Don't gamble with the SNP when you can guarantee change with Labour."
Mr Miliband hit back at Ms Sturgeon's claims that if Labour fails to work with Scottish nationalists this would see David Cameron win a second term as Prime Minister.
He added that if the SNP wins dozens of seats from Labour in Scotland - as opinion polls have suggested - this would increase Tory chances of being the largest party.
Mr Miliband vowed: "I will never put the Tories into government. I have spent my entire political career fighting them.
"But the tragedy is that the SNP may very well might let the Tories in. That's what could happen if the Tories are the largest party."
He continued: "I am also clear there will be no deal, no pact, no coalition, no tie-in with the SNP.
"I don't say that for tactical reasons - I'm advocating this for principled reasons.
"We cannot do a deal with a party that wants to break up the UK when we want to build it up."
A second independence referendum is the only thing the SNP wants, he claimed, adding: "That's their priority. That's their promise. But it is not ours. Our priority is social justice."
Mr Miliband said Labour believes in "the principles of sharing and solidarity that underpin the partnerships of four nations that is the modern UK".
He added: "If we set England against Scotland, if we set any part of our country against another, it does not help working people, it harms working people.
"It undermines the ability to share resources. It drives down wages and conditions in the race to the bottom.
"Nationalism doesn't understand we are stronger, not weaker, when we look after each other across the whole of our country.
"Nationalism never built a school. It never lifted people out of poverty. It never created a welfare state that healed the sick and protected our most vulnerable. Nationalism cannot create the jobs we need."
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