David Cameron today spoke out in defence of the union under the slogan "stronger together".
Speaking as the leader of the Conservative and Unionist Party, Mr Cameron said an imperfect union was preferable to a broken one.
Although he said there were legitimate constitutional questions posed by the relationship between Scotland and England - most notably by the West Lothian question - Mr Cameron said the Tories would not be jumping on the "Barnett formula bandwagon".
Mr Cameron's speech suggests the Tories will not, as first thought, seek to gain political advantage from the potential anomaly of a Scottish prime minister.
Instead, appearing alongside Scottish Conservative leader Annabel Goldie, the Tory leader today turned his attention to the leadership north of the border.
He hit out at SNP calls for independence within the decade and also attacked the factions in England supporting calls for increased independence.
Mr Cameron said politicians must not allow the "legitimate and affectionate" doubling up of patriotic pride - where people are proud to define themselves as both Scottish and British - to be pushed aside by a "course and casual nationalism".
Speaking in Edinburgh, Mr Cameron warned the future of the union now looks more fragile than at any other time in recent history.
He said: "We must confront and defeat the ugly stain of separatism seeping through the Union flag."
Mr Cameron called on politicians to create a positive vision of British society in order to renew a sense of belonging.
The Tory leader claimed Britishness is already one of "the most successful examples of inclusive civic nationalism in the world," describing it as a "shining example" of what a multi-ethnic, multi-faith and multi-national society can and should be."
But he hit out at Gordon Brown's attempts to foster a debate on "Britishness" through focus groups and debates on mottos and national anthems.
The prime minister approaches the question of national identity "like a brand manager trying to launch a new product on the market", Mr Cameron said.
His renewed defence of the union comes as a new opinion poll shows fewer than two in five people define themselves as British.
An ICM poll for the Telegraph found, however, that 69 per cent of people want to support the union with 24 per cent agitating for separation.