Gordon Brown has attacked David Cameron for "whipping up English nationalism" in a bid to win the General Election, as well as slamming the SNP's offer to help Ed Miliband get into Downing Street as disingenuous.
The former prime minister said the Tories were fanning flames of hatred between the English and the Scottish, in what he called a cynical attempt to get people to vote for them out of fear of a Labour-SNP deal.
Speaking to a group of supporters in Fife last night, Brown said: “The only way they can win is to build resentment in Scotland of the English and resentment in Scotland of the English," Politics Home reported.
Brown accused the Tories of fanning nationalism in an "off the cuff" speech
The Conservative election campaign has focused heavily on warning against what it has described as a “coalition of chaos” between Labour and the Scottish Nationalists.
Cameron has described the idea of a Labour government propped up by the SNP as a "match made in hell".
Brown's intervention comes after Former Tory Scottish Secretary Lord Forsyth said that his own party had a "short-term and dangerous" approach to Scotland, which threatened the union of the UK.
Brown is credited by some as having saved the 'No' campaign during the Scottish independence referendum by giving the "speech of his life" passionately defending the United Kingdom.
The intervention is one of his first in the General Election debate around Scotland, where Labour is widely-expected to lose most of its seats to the SNP. Brown said that large numbers of SNP MPs could mean “months of constitutional chaos” for the UK.
The former prime minister also attacked the SNP in Fife, suggesting the party was misleading people over its offer to help Ed Miliband into Downing Street.
He implied the nationalist party was over-exaggerating the power they would wield working with a Labour-led administration, claiming: “People must realise they are not interested in a Labour government.”
A Labour source told The Huffington Post UK Brown's speech was "off the cuff" and unprepared.
Discussion of Scotland is overwhelmingly dominating the election, taking 33% of the online conversation, according to social media analysis from Bell Pottinger on Thursday, while traditional vote-winning topics like the economy, health and immigration have fallen behind.
Most-discussed General Election topics on social media
Brown also told the audience that a Labour government would be the only one to “immediately deal with food bank poverty, zero hours poverty, inequality and the NHS”.
In a letter to voters today, Brown also said Labour is ready to reclaim its "historic role as Scotland's party of fairness and social justice".
The Tories are committed to billions of pounds of austerity and the SNP's plan for full fiscal autonomy would leave a £7.6 billion hole in Scotland's economy, he claimed.
But Scottish Deputy First Minister John Swinney said the SNP is the only party pledging investment in jobs and services, in contrast to the "Tory-Labour austerity alliance".
Brown said in the letter:
"Labour is proving itself ready to reclaim its historic role as Scotland's party of fairness and social justice - committed to tackling youth unemployment, widening educational opportunity and ending the need for food banks."
"If they win the election, the Tories are committed to billions of pounds more austerity - which means less money for Scotland and our NHS.
"The SNP's own spending plans for the UK confirm that next year they would not spend a single penny more than the Tories.
"And the nationalists would scrap the Barnett formula, meaning that our NHS and other public services could only be funded by taxes raised in Scotland. That would mean additional cuts of £7.6 billion to the services we all rely on.
"The Labour Party created the NHS. We built the NHS. And we have always ensured that it has been fully funded."
But Swinney said in response: "Westminster's cuts have been holding back our economy and hurting people in our communities for too long - pushing 100,000 more children in Scotland into poverty and seeing the numbers of people forced to rely on food banks shooting through the roof.
"Ending austerity is without doubt the key issue of this General Election campaign - and both Labour and the Tories are on the wrong side of people in Scotland and many people across the UK. Austerity has failed on every measure - and it's time for a new, more progressive approach
"The contrast between the Tory-Labour austerity alliance and the SNP's plans for investment could not be clearer - and is one of the reasons that more and more people in Scotland are putting their faith in the SNP as we approach the General Election."