David Cameron has claimed that English "ignorance" of Scotland is putting the future of the United Kingdom at risk.
In a speech in Glasgow on Friday the Conservative leader argued that a lack of "respect" towards Scots is playing in to nationalist hands.
Following Gordon Brown's defence of the union last week, in which the chancellor stressed the economic benefits of the union, Cameron said better arguments against independence must be developed ahead of Holyrood elections next year in which recent polls have suggested the SNP could see an increase in support.
"The chancellor made some valid points about the economic case for the union," he said. "But the case for the union isn't just economic.
"I don't believe that, in the 21st century, Scotland will be cowed or intimidated into remaining part of the UK through fear of the economic consequences of going it alone.
"Those of us who believe in the union have got to do better than that.
"We need to make a positive case for Britain that speaks to the heart as well as the head."
Cameron has provoked criticism for saying that he wants Scottish MPs in Westminster to be stripped over their right to vote on English-only laws.
But he argued that the relationship between England and Scotland needs to be based on equality.
"There's one aspect of Scottish-English relations that I want to address," he said.
"It may seem trivial to some but I happen to believe that it's almost more damaging to the union than institutional or economic difficulties.
"It's a question of attitudes, and in particular the ignorance of English people about Scots and Scotland.
"Why should this matter? After all, we've all got broad shoulders.
"Well it matters because the union is supposed to be a relationship of equals.
"Not in terms of size obviously - but certainly in terms of that most precious of commodities, respect."
He claimed that the lack of respect is shown in "Russ Abbott-style" stereotypes, successful Scottish sportsmen being claimed as "British" and Scottish money not being accepted in English shops.
However he acknowledged that the "Conservatives have a particular hurdle to overcome" after almost being wiped out as a Scottish political force in the 1980s and '90s following the experiment with introducing the poll tax north of the border and Tory opposition to devolution..
"Surveying the political landscape, we need to ask ourselves a simple and stark question: How did it come to this?" Cameron said.
"We hold one Scottish seat out of 59 in the UK parliament. 17 seats out of 129 at Holyrood. And we control one Scottish council out of 32. That's pretty dismal.
"A series of blunders were committed in the 1980s and '90s of which the imposition of the poll tax was the most egregious."
But he insisted that under his leadership the party would not turn its back on Scotland even if separation made it easier for the Tories to win power at Westminster.
"As we prepare for the elections to the Scottish parliament next year I've got a message for the people of Scotland," Cameron declared.
"Yes, we opposed devolution - but the world is very different now and the Conservatives are determined to make a success of Holyrood.
"Yes, we centralised too much in the past - but today we're serious about giving decision-making power to local people and local communities.
"Yes, we made mistakes - but we've faced up to them. I understand what needs to happen.
"If I become the prime minister of the United Kingdom, I'll never, ever take Scotland for granted. Every part of Britain is entitled to full and equal respect."
