Winning the emotional battle over the ties that bind Scotland to the rest of the UK will be crucial in the independence referendum contest, David Cameron has said.
The Prime Minister said there were "arguments of both the head and the heart" that needed to be made as he claimed Scotland would be worse off on its own.
But as well as the economic argument, Mr Cameron insisted that the campaign to preserve the union must also win the fight for the hearts of Scottish voters by showing "we are stronger together".
Mr Cameron's comments, at a joint press conference with his deputy Nick Clegg to mark the Westminster coalition's mid-term review, came after figures showed Scots would be £1 worse off each year under independence, using an analysis of oil revenues over the course of devolution.
The analysis produced by Treasury Chief Secretary Danny Alexander was intended to expose the SNP claim that people would be £500 better off a year as a "myth" but independence campaigners seized on the £1 cost as being a "price worth paying".
Mr Cameron said he expected that the No campaign would be able to show "categorically" that Scotland would be worse off. He said: "I think there are important arguments of both the head and the heart that need to be made in this great debate about the future of our United Kingdom and I profoundly hope that Scotland will vote to stay in the United Kingdom.
"I think when it comes to the arguments of the head, things like would Scotland be better off, I think we will be able to show, categorically, that Scotland would be worse off, would be less well off."
He said there would be a changing pattern as North Sea oil runs down and also said there would be uncertainty over jobs in the defence and financial services sectors if Scots voted for independence. But Mr Cameron insisted the financial considerations were only a part of the decision facing the Scottish people.
"There are arguments of the head, but I profoundly believe we must win not only the arguments of the head but also of the heart: that we are better off together in the United Kingdom, there's a solidarity that we show each other, if different parts of the United Kingdom have a difficult time we are all there ready to stand behind those parts of the United Kingdom.
"We are stronger together, we are better off together, we are safer together. So those heart arguments will also, I think, win the day."