The SNP's plans for public services after independence would cost Scots at least an extra £3,100 a year, Scottish Secretary Alistair Carmichael has suggested.

Mr Carmichael said proposals for Scandinavian-style systems would require the introduction of Denmark-level high taxes.

The Liberal Democrat MP said the extra thousands of pounds would see Scots go from paying an average of under £10,000 a year to more than £13,000.

But the true cost could be even higher as the average Scots would also lose a £1,400 a year "union dividend", he said, a figure that the SNP rejects.

Last night Scottish Finance Secretary John Swinney accused Mr Carmichael's Conservative-Lib Dem Coalition of posing a biggest threat to Scottish public services: "Only a Yes vote in September will allow Scotland to protect key public services, including our NHS, from Westminster cuts and a Tory-led privatisation agenda.

"More and more people are waking up to that fact, and to the huge opportunities an independent Scotland will offer - which is why support for a Yes vote is increasing by the day." Mr Carmichael had earlier called on Scottish ministers to tell Scots how much extra they would have to pay as he warned that it was impossible to build "castles in the sky".

He is not the first politician to warn that the SNP's public service plans could cost more.

The pro-independence campaign leader and former Labour MP Dennis Canavan has predicted that Scots would be willing to pay extra to create a fairer Scandinavian-style state.

But the Scottish Government has said that there are no plans for tax increases after a Yes vote.