David Cameron says he would use both "heart and head" to urge Scotland to remain part of the UK, with a referendum for Scottish independence likely to take place in 2014.
Cameron says the current system offers Scotland "the best of both worlds", advising them not to break the 300-year-old union.
"Put simply: Britain works. Britain works well. Why break it?" writes the prime minister on the No 10 website.
Cameron goes on: "It's about heart because our nations share a proud and emotional history. Over three centuries we have built world-renowned institutions like the NHS and BBC, fought for freedom and democracy in two World Wars, and pioneered and traded around the world."
Cameron's remarks come as his Conservative-led coalition government prepares to release its first analysis paper on Scotland's contribution to Britain.
However, Scottish National Party (SNP) leader Alex Salmond is determined to see his flagship policy fulfilled. If Scotland leaves the union, it will have serious ramifications for the rest of the UK.
Although Cameron concedes that it is the Scots' right to remain in the UK, he has pledged to furnish the "facts" before the referendum.
"As one of Scotland's two governments, the UK government has a duty to help inform people with hard facts. So we'll be providing expert-based analysis to explain Scotland's place within the UK and how it might change with separation - and our first paper is published tomorrow," writes Cameron.
The SNP published a document earlier this week providing a "road map" for the transition in Scotland soon after independence. The "transition plan" says if Scotland secures a "yes" vote in the referendum, independence day could be celebrated in March 2016.
Criticising the transition proposal, Cameron said: "I know those arguing for independence are already preparing their separation transition plan, as though they've got this in the bag, but to me that is wrong. It's like fast-forwarding to the closing credits before you've been allowed to see the movie."
Cameron's remarks have been criticised by Scotland's deputy first minister Nicola Sturgeon, who said the prime minister is "simply continuing with an entirely negative attack".