The SNP leadership should be prepared to submit to a vote of confidence at Holyrood if they lose the independence referendum, according to the Tory deputy leader.

Jackson Carlaw made the call in an attempt to force First Minister Alex Salmond and Deputy First Minister Nicola Sturgeon to explain what they would do if voters say No on September 18.

Unionist parties are repeatedly urged to spell out what they will do in the event of a No vote, he said at the Scottish Conservative party conference in Edinburgh.

But the SNP will have "nothing to offer" if people do not back independence, he said.

"At the very least, the very least, having put the real business of Scotland on hold for three years, the First Minister and his deputy must submit themselves to a vote of confidence at the first opportunity after the referendum in the Scottish Parliament, on Tuesday September 23," Mr Carlaw said.

"The Scottish Parliament is there to hold ministers to account, and once this referendum is over and the true cost that this needlessly long and drawn out referendum has been realised, it must do its job, and the two people who masterminded it must be made to face the consequences of their decisions. Thereafter, the electorate can do likewise in 2016."

The Conservatives are currently looking into what they may offer after a No vote.

Prime Minister David Cameron said yesterday that the Scottish Parliament could gain more power over tax if voters reject independence.

The pro-independence Yes Scotland campaign group immediately branded Mr Cameron's promise a sham.

And an SNP spokesman said: "This is just silliness from Jackson Carlaw. With the polls narrowing and support for Yes increasing he might want to dust off his last Tory leadership campaign instead of continuing this obsession with the SNP.

"The latest poll put support for Yes at its highest since last summer, with the gap now down to single digits, and therefore we are confident of success in September."