David Cameron vowed to fight for "our country's life" on Thursday - but hours later admitted there had been “much progress" in talks with Scottish first minister Alex Salmond.
The prime minister met with the SNP leader in Edinburgh, after giving an impassioned speech making the case for the United Kingdom to stay together.
However, after the meeting, Cameron told the BBC: "On the issue of independence, separating Scotland, leaving the United Kingdom, I am afraid there wasn't much progress.”
He said: "I believe that we need to put a straightforward and simple and legal question to the Scottish people in good time, which is to ask the straightforward question 'Do you want to stay in the United Kingdom...' - and I hope that is what people will vote for - '... or do you want to leave the United Kingdom?'"
Earlier in Cameron's speech, he acknowledged that the Conservative Party was not popular in Scotland - it has only one MP north of the English border - and said he had to show a "little humility".
But he dismissed suggestions that he would be happier to see Scotland break away as it would make it easier for him to form a majority government in Westminster as the prime minister of just England.
"I'm not interested, I don't care, that's not the job I want," he said.
Speaking in Edinburgh on Thursday afternoon, the prime minister said the break-up of the UK would create "artificial barriers between" England, Scotland, Wales and Northern Ireland.
"Our Union isn’t some antique imposition. It’s living, free and adaptable. It’s admired around the world as a source of prosperity, power and security," he said.
"In an increasingly uncertain world, where risks proliferate and atomisation threatens our ability to look out for one another nothing encapsulates the principle of pooling risk, sharing resources and standing together with your neighbour better than the United Kingdom.
"We’re stronger, because together we count for more in the world, with a permanent seat on the United Nations Security Council, real clout in NATO and Europe and unique influence with allies all over the world."
First Minister Alex Salmond, meanwhile, called on the PM to explain hints about further devolution in his speech: “I think as we go into this exciting debate about independence for our country, it’s incumbent on me as first minister of Scotland to spell our what independence means for the Scottish people, but it’s also incumbent on the prime minister and his allies, the anti-independence parties to spell out what they’ve got in mind.”