The challenge came when he launched the latest stage of the Scottish Government’s National Conversation on the country’s constitutional future.

A separate commission, chaired by Sir Kenneth Calman, is reviewing the powers of the Scottish Parliament ten years on from devolution, with the involvement of Labour, the Lib Dems and the Tories – but independence has been excluded from its deliberations. Mr Salmond yesterday argued there was now consensus that the present constitutional framework did not give Scotland the opportunities it needed to succeed.

He said he was "relaxed" about the commission set up by the other parties. But he said: "I have already said that as First Minister I am happy to test support for enhanced devolution, along with support for independence for Scotland.

"And I say to those who oppose the restoration of Scottish independence that just as I respect absolutely their right to hold that view, so in return I feel able to require of them a clear alternative which can be put onto a ballot paper and held up to public scrutiny and be available for a decision by the Scottish people."

Scotland Office Minister David Cairns later claimed the preference voting move was a "humiliating" U-turn by Mr Salmond. "He is running scared of voters," said Mr Cairns. "What has happened to his Braveheart stance?"

But a spokesman for Mr Salmond said he was breaking no new ground.

"In all the many years the SNP have talked about a constitutional multi-option referendum it has always been on the basis of a preferential voting system," he said.