David Cameron called on Scots to drape themselves in "red, white and Saltire blue" as he set out the Conservative goal of overtaking Labour to become the official party of opposition at Holyrood.
He said his party had delivered "real devolution" for Scotland, keeping the United Kingdom together.
Elections to the Scottish Parliament take place in two months time and the Prime Minister insisted it was only the Tories who spoke for all those who had voted against independence in the 2014 referendum
With Scottish Labour support collapsing, he said the Scottish Conservative must change from being the "effective opposition" to the SNP at Holyrood, and instead "fight to become the official opposition".
He said that while "it has never been easy" for Tories north of the border, the party had the advantage of its "absolute star" Scottish leader Ruth Davidson along with "Labour's collapse".
The SNP Government in Edinburgh was branded "arrogant and overbearing", he told the party's Scottish conference in Edinburgh: "Let's make this our moment. Let's drape ourselves in red, white, and Saltire blue."
Mr Cameron said: "In 2016 when we face some really tough elections and the SNP lack any sort of scrutiny from the second largest party, we can be the ones that give Scotland the strong alternative it needs.
"That's right, we the Scottish Conservative Party. Today we are the effective opposition and for the next 62 days we're going to fight to become the official opposition."
While Nicola Sturgeon's SNP continues to dominate the opinion polls in Scotland - with the party seemingly on track for another majority government in May - Mr Cameron said the Conservatives are the only party capable of challenging them.
"With Labour's collapse, Scotland is in danger of becoming a one-party state," he said.
He hit out at the SNP's "litany of failure" since coming to power in 2007 and added: "It falls to us, the Conservatives, the only party fit to expose these spendthrift, out-of-touch, dogmatic, inept nationalists for what they really are."