In a rousing speech to Scottish delegates at the Tory party conference in Birmingham, Mr Cameron vowed to end the SNP's monopoly of Scottish identity.
It came as Scottish Conservative leader Ruth Davidson blamed Alex Salmond for a poll which revealed supporters of No to independence have opened a 25-point lead over the Yes campaign.
Mr Cameron said he will seal the deal on the terms of the 2014 referendum in a meeting with the First Minister next week, as revealed by The Herald yesterday.
He said: "I want to tell you from the bottom of my heart there are lots of things I want this Coalition Government to achieve. There are lots of things we are achieving. And you've heard about many of them at this conference this week. About how we have taken millions of people out of tax, about how we have done right for our pensioners, about what we are doing to safeguard our NHS and about what we want to do for our armed forces. But, frankly, it's hard to think of anything more important for a Conservative than keeping our United Kingdom together."
Mr Cameron stressed how the pro-UK campaign had not only to win the battle of the head but also the battle of the heart.
He declared: "Do not let us for one minute leave to the SNP the arguments of Scottish identity, Scottish passion, Scottish history and Scottish culture.
"Don't let them wrap themselves in the flag and own the identity of Scotland because you can be more proud as a Scot than as a Brit but still believe head, heart and soul in this incredible partnership we have forged over these years and all we have done together."
Mr Cameron, who is likely to meet Mr Salmond at St Andrew's House in Edinburgh on Monday, said: "We are going to be able to reach a proper agreement about what is right and proper for Scotland, which is to have a fair, decisive and legal referendum on whether Scotland wants to remain in the UK or if it wants to separate and be independent".
Mr Cameron explained that, after the 2011 SNP landslide, it was only right and proper the Coalition should be "fair and honest brokers" and deliver the promised referendum.
However, Mr Cameron stressed the poll "has to be a single, simple question about whether Scotland wants to stay or go – and I'm sure we will achieve that". He insisted the debate about Scotland's future could now begin.
Mr Cameron made clear that, while there would be major disadvantages for Scotland if it decided to leave the UK, there would also be "bad consequences for the rest of us, for England, Wales and Northern Ireland; we want Scotland to stay because we believe we are all stronger together and we would be weaker apart".
Mr Cameron was cheered by delegates when he mentioned the TNS-BMRB survey that revealed 53% of people would vote No to independence, compared to 28% who are in favour of breaking up the United Kingdom.
Ms Davidson said: "The big beast of Scottish politics, Alex Salmond, has managed to cut support for his one big issue by one-quarter in all the time he has headed up his party. Indeed, every time he opens his mouth it seems support [for independence] goes down."
Nicola Sturgeon, the Deputy First Minister, said: "It is becoming clearer by the day the Tory-led anti-independence campaign has no alternative to independence, other than more and more cuts imposed by Westminster, and as this debate develops, we are extremely confident support for independence will grow and we will achieve a successful Yes result in autumn 2014."
Labour's Patricia Ferguson said: "The more people hear about separation from the SNP, the more they realise we're better together."
Willie Rennie, the Scottish LibDem leader, said the Nationalists were "failing to come up with the most basic answers to simple questions that people are posing".
l Liam Fox, the former Defence Secretary, will today claim the SNP's "pick'n'mix" approach to the armed forces will leave the army of an independent Scotland "without any supporting arms, an air force without any transport aircraft or tankers and a navy without a fleet auxiliary".