David Cameron has accused SNP leader Nicola Sturgeon of selling a “false dream” of separation to the Scottish people and predicted it would “fade” over time.
The Prime Minister admitted that the parties that believe in the union would have to fight hard and conceded he could see there was a nationalist appeal.
But he added: “I think this dream will fade.”
He told BBC Radio 4’s Women’s Hour: “My view is she’s selling a dream, but it’s a false dream. She’s selling the dream of separation.
“I can see there’s a nationalist appeal, but I profoundly believe we are so much better off as a United Kingdom.
“Sometimes in politics, dreams and visions can be terribly exciting and enthuse people.
“But when you go to the numbers … there are huge holes in her case.
“I think this dream will fade, but it’s going to take some time and the parties like mine that believe in the UK are going to have to fight very hard.”
Asked whether he could see Ruth Davidson, leader of the Scottish Conservatives, in overall charge of the party, Mr Cameron said he did not want to put a limit on her ambition, adding: “I think she’s extremely effective.”
At the suggestion he is pragmatic rather than a dreamer, he replied: “The practical things I care about … these may be down to earth and practical, but I’m deeply passionate about them and I think they are the things that matter the most.
“Just because we are not ideologues … don’t think we don’t care massively about the future of this country, about the families within it and about the security for people we want to deliver.”
The Tory leader was also asked to justify going to Saudi Arabia after the death of King Abdullah to pay his respects.
He said: “I don’t agree with the Saudi approach on many of these issues.
“When there are cases of human rights abuse for instance we raise them with great vigour.”
But he insisted the relationship mattered in light of the shared aim of stability in the Middle East.