Alex Salmond has repeatedly been challenged to reveal if legal advice has been taken to back up claims from SNP ministers that Scotland would still be part of the EU if it left the UK.
Labour leader Johann Lamont said the First Minister so far "fails to provide a single shred of evidence" on the subject.
She challenged him on the issue at Holyrood the day after the President of the European Commission stepped into the row over an independent Scotland's place in the EU by saying all new states have to apply for membership.
Jose Manuel Barroso said: "A new state, if it wants to join the EU, has to apply to become a member of the EU, like any state."
Today, Mr Salmond pledged that when the white paper on independence is published in a year's time, "these areas of continuing European membership for an independent Scotland will be examined in great detail".
He said this would happen "a full year before the decision on the referendum", adding: "Everything in that white paper will be fully consistent and informed by the legal advice that we receive."
Mr Salmond again insisted Scotland would still be part of the EU if it were to become independent.
"Scotland is part and will remain part of the European Union as an independent country," the First Minister said.
Yesterday, Mr Barroso told BBC Radio 4 he would not speculate now about possible secessions within existing states, such as the UK.
But he added: "To join the EU, yes, we have a procedure and it is a procedure in international law. A state has to be a democracy and has to apply to become a member of the EU. All the other member states have to give their consent."
Ms Lamont pressed Mr Salmond on the issue at their weekly Holyrood clash at First Minister's Questions.
The Labour leader said Mr Barroso "was clear when he said 'a new state, if it wants to join the European Union, has to apply like any state"'.
She argued: "That means that the new state of Scotland would first have to apply to be a member of the European Union and, if successful, adopt the euro as our currency."
She challenged Mr Salmond to say if he had any legal advice which contradicted Mr Barroso's comments.
The First Minister responded: "Scotland is not an accession state, we've been members of the European Union for 40 years.
"We are not in the position of a country which is not part of the European Union, and that means of course there have to be negotiations, but the crucial point is that these negotiations take place from within the context of the European Union."
Ms Lamont hit back by saying if Scotland would not be a new state "you wonder what they (the SNP) have been arguing for for the last 100 years".
She urged him to make public any legal advice the Government had on the issue.
"If the First Minister has advice which does contradict what President Barroso has said, why does he not remove all doubt and publish it?" she asked.
"Dialogue between the people and their representatives is essential in a genuine democracy."
With the Scottish Government appealing an official ruling compelling them to reveal whether they have taken legal advice on the issue of Scotland's future in the EU, Ms Lamont told the SNP leader: "Instead of telling the people of Scotland what advice he has had, he is using our money to fund a court action to stop us knowing what the First Minister knows."
Ms Lamont said Information Commissioner Rosemary Agnew had "ruled it is in the public interest to know what information has been taken into account in developing policy in such a significant issue".
She demanded: "Surely the First Minister believes it is in the public's interests to know the consequences of voting for independence?"
Mr Salmond, however, argued there was a difference between the "40 years of membership of the European Union" which Scotland had had and a "country which is trying to join the European Union for the first time like Turkey".
He again said an independent Scotland "quite clearly will remain part of the European Union and negotiations will take place from within that context".
He also said he would be breaching the ministerial code by disclosing legal advice on the issue.
"The fact that legal advice has been given to ministers or its existence must not be revealed outwith the Scottish Government unless under some clear circumstances," the First Minister told her.
However, he added: "I do believe I have a solution for Johann Lamont which reconciles my obligation within the ministerial code and, I believe, the democratic imperative of information for the people of Scotland.
"We have set out our intention to publish the white paper on independence this time next year.
"I give her my guarantee that that white paper, which sets out the full context of the independence proposition, will contain a detailed assessment on the particular question of membership continuing of the European Union.
"I give her the guarantee that everything in that document will be fully consistent with the legal advice that we receive."
Mr Salmond stated: "That seems to me a reasonable solution of how we can reconcile the requirements of the ministerial code with, I believe, the imperative to let the people of Scotland see the full advantages of being an independent county."
With the Scottish Government challenging the Information Commissioner's ruling in the courts, Ms Lamont said it was costing £100,000 to keep that information out of the public domain.
She told Mr Salmond: "I'm not sure who the First Minister imagines would refer him under the ministerial code to give us information it is costing £100,000 to keep away from us."
She hit out and said: "Meaningless assertion on the pound has descended into deliberate deception on the euro.
"While Alex Salmond fails to provide a single shred of evidence, President Barroso does - Scotland would have to reapply to the EU and join the euro with all the disastrous economic consequences that would have.
"Alex Salmond has to understand although when he says something his backbenchers agree, we expect more than simple assertion.
"He refuses to tell the people of Scotland the truth. When is he planning to tell them - now, never or when it is too late?"
Mr Salmond said Mr Barroso had said "no such thing" about the euro.
He added: "I offered what I think is a reasonable solution to these matters, to conform to the ministerial code and provide the information that the people wish to have. And that is on the publication of the white paper, a full year before the decision on the referendum, these areas of continuing European membership for an independent Scotland will be examined in great detail.
"Everything in that white paper will be fully consistent and informed by the legal advice that we receive.
"That seems to me a pretty reasonable proposition and folk in Scotland will be looking forward to reading that white paper, the passport to independence and freedom."
Scotland will be taking "a step in the dark" on referendum day unless ministers publish their legal advice about Scotland's future in the EU, according to Liberal Democrat leader Willie Rennie.
"There is a great deal of confusion about his plans for Scotland in the EU," he said. "Asserting something doesn't actually make it true. The First Minister says he's right and Scotland will be a continuing member. But what if he's wrong?"
Mr Salmond said: "He will have heard his former colleague Lord Wallace support the Scottish Government's position in terms of the legal advice by pointing out he would face exactly the same circumstances as a Westminster minister."
Speaking on BBC Radio Scotland`s Good Morning Scotland programme last month, Lord Wallace said that under the UK ministerial code "law officers' advice is neither confirmed nor denied".
The Scottish ministerial code states that ministers should always take account of the public interest in maintaining the right to confidentiality of communications between legal advisers.
The code states release of the content of legal advice is likely to be appropriate "only in highly-compelling cases".
Mr Salmond added: "I'm quite certain that Willie Rennie, given Lord Wallace's comments, will understand that the ability to reconcile the provisions of the ministerial code with the imperative of information to the people of Scotland is one where I think assuring that the White Paper will contain the information consistent with legal advice provides a satisfactory solution towards."
Mr Rennie added: "But there's clearly a dispute about that legal advice, and if voters opt for independence they may well find out that we have lost the rebate, we are forced to join the euro, and the Schengen agreement."
Faced with jeers from the SNP benches, he continued: "That's the reality. That is the consequence if the First Minister is wrong, so when is he going to get clarity on this?
"When is he going to start negotiations and discussions with EU members about the way ahead on this?
"Because we need clarity. It can't just be a step in the dark based on his assertions."
Mr Salmond said: "I thought the call was for the publication of our legal advice - the issue in these questions. He seems to be doubting the legal advice even before its publication.
"I do think the process of publishing the White Paper consistent with legal advice will satisfy even Willie Rennie in terms of the bona fides."