Alex Salmond is preparing to stage a referendum on Scottish independence that will offer voters a second option – full financial autonomy while remaining part of the United Kingdom.

In an exclusive interview with the Guardian, the first minister said that allowing Scotland to have fiscal autonomy without full independence was “a very popular option” with “plenty of evidence” of public support. “I think there’s a case for that. The case is essentially a democratic case,” he said.

His move towards staging a two-question poll comes after several weeks of mounting pressure from David Cameron and Nick Clegg to clarify his plans for the referendum, which is due to take place in 2014 or 2015.

Although he confirmed that he expects 16- and 17-year-olds will be allowed to vote in the referendum, for the first time in British electoral history, Salmond has so far refused to publish details about the proposal, including the exact questions.

During last week’s Tory party conference, Cameron taunted the first minister for his reticence, accusing him of being a “big feartie”, running scared of the voters, because he knew independence did not have majority support. At the Liberal Democrat conference, Clegg challenged Salmond to have “the courage of his convictions” by holding a single-question “yes or no” referendum.

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