ALEX Salmond has given his strongest hint yet there will be two questions in the independence referendum, by saying the Scottish people have a fundamental "right to decide" on whether Holyrood should have full tax powers, known as devo max.

The First Minister, who until now has confined his comments to saying he is open-minded about a second question, also said there was a "very attractive argument" for devo max.

The remarks, made recently in America, come amid growing speculation that Salmond intends to defy Westminster by including a second question about enhanced powers in the 2014 ballot.

Opinion polls consistently show more Scots support extra powers for Holyrood over independence.

Devo max offers Salmond a way to avoid defeat in a straight Yes-No referendum, as well as being a major stepping stone to independence.

Pro-Union parties say a second question is a desperate SNP fallback, which would muddy the issue of Scotland being in or out the UK, and could expose the referendum to legal challenge.

The UK Government, which wants a simple Yes-No on whether Scotland should leave the UK, has offered Edinburgh a new power, known as a Section 30 order, to make the referendum immune from legal challenge.

But there is a catch: Salmond can only have the new power if he sticks to a single question, the question Westminster thinks he will lose.

In return, Salmond has said he will accept the Section 30 power, but won't accept any strings attached, leading to an impasse. But the Sunday Herald has learned Scottish ministers now believe a two-question consultative referendum held by Holyrood would be legally "watertight", despite Westminster warnings.

Officially, the SNP Government says it will not make up its mind on whether to have one or two questions until the autumn, once it has analysed the 22,000 responses to its consultation on the referendum.

But with polls showing support for independence stalling, Salmond appears to face a choice between offering voters devo max or losing a Yes-No vote, even if this provokes London and dismays independence diehards in his own party.

The SNP Government defined devo max in a 2009 paper called Fiscal Autonomy in Scotland. It would see Holyrood take responsibility for the vast majority of tax and spending, with Edinburgh paying London for "shared services" such as defence, foreign affairs, and social security.

VAT, financial regulation, and employment and competition law would stay the same across the UK.

But essentially all other taxes and benefits would come under Edinburgh control, including Scotland's geographic share of North Sea oil.

Now the Sunday Herald has obtained a recording of Salmond in a question-and-answer session at the Commonwealth Club of California in San Francisco a fortnight ago, in which he talks up devo max.

The Scottish Government put Salmond's speech at the event online, but omitted the Q&A session.

Asked whether he was committed to a straight Yes-No on independence, or might offer devo max, Salmond told the audience: "There's a view abroad in Scotland that perhaps it would be better from where we are now - where we now control about 16% of Scotland's revenue base, that rather than become an independent country, at least in the first stage, that that fiscal base should increase to something near 100%, and that's often called devo max or fiscal autonomy. And it's a very attractive argument, incidentally.

"It has a major problem, and that is that the UK Government, while they respect the right and the ability of Scots to decide on independence, are not prepared to accept the right of the Scottish people to decide on devo max. They say that devo max should not be on the ballot paper. My position is a bit different from that.

"My concern as First Minister of Scotland is to make sure the independence question is on the ballot paper and fairly asked - But I'm open to persuasion that there should be a second question, as it's called, so people should be asked, 'Do you want independence?' And if it's not answered Yes, 'Would you like fiscal autonomy, or devo max, or fiscal responsibility?'"

Salmond's pro-Union rivals said the comments betrayed his fear over losing the referendum.

Scottish Labour leader Johann Lamont said: "The fact Alex Salmond wants a second question shows he has given up on winning the first."

Scottish Tory leader Ruth Davidson added: "This is further proof that Alex Salmond is secretly plotting to get a second question on the ballot paper because he knows he is losing the argument to rip Scotland out of Britain."

A Scottish Government spokeswoman said: "The First Minister's position on this issue has never changed and what he said in the US is consistent with that."