Almost a third of Scots currently support independence, according to an independent survey.
Researchers from YouGov found 30% of people want Scotland to leave the United Kingdom, while just over half (54%) do not and 16% were undecided.
The SNP claimed the results show that support for independence is now higher than it was when the party won a landslide victory at Holyrood last May.
But Scottish Tory leader Ruth Davidson argued the poll is "further proof that Alex Salmond is losing the argument on separation, with fewer people by the day buying into his vision".
She said: "The SNP's dithering on the issue of a second question is putting voters off. Like all parties involved in this argument, they want a fair, legal and decisive question on the ballot paper. Anything else would muddy the waters and make a mockery of the SNP's manifesto pledge."
With a vote on independence likely in autumn 2014, Ms Davidson said: "I am confident that when the time comes, Scotland will reaffirm its commitment to the United Kingdom."
YouGov conducted the research for the Fabian Society, questioning 1029 people in Scotland between July 17 and 20.
People were asked if they support or oppose Scotland becoming independent from the rest of the UK.
The Scottish Government's preferred wording of the question for the independence referendum is: Do you agree Scotland should be an independent country?
An SNP spokesman said the most recent poll that put this wording to voters showed that 36% back independence.
"In terms of this YouGov poll, support for independence is higher than when the SNP won our landslide election victory last year, and the gap with support for the Union has narrowed by five points, which is very positive," he said.
"We believe that the vast majority of people in Scotland prefer home rule with independence to Tory rule from Westminster, and we are confident of achieving a Yes vote in autumn 2014."
The poll also asked people about their Westminster voting intentions, with 43% voting for the Labour party, ahead of the SNP on 29%, the Tories have the support of 15% and the Liberal Democrats 7%.
The SNP spokesman said: "The poll also shows that SNP support is 9 points higher than in the 2010 Westminster general election and the most recent poll to ask about Scottish Parliament voting intentions put the SNP at 47%, even further ahead than in our landslide election victory last May."
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