THERE has been an odd bout of recrimination of late within the side that is well ahead in the polls.

Better Together and its leader Alistair Darling have come under friendly fire from so-called "senior sources" in both the Tory and Labour high commands for the performance of the No campaign.

This is strange, given the widespread media monstering of the Scottish Government's White Paper on Independence and the continuing lag in the polls by the Yes campaign. Why should the pro-Union side be jittery?

Part of that has to be the fact that they are up against such formidable opponents in First Minister Alex Salmond and his deputy, the "Yes Minister" Nicola Sturgeon.

Her perceived defeat of Michael Moore in a live televised debate was widely seen as costing him his job as Scottish Secretary. Her next opponent, deputy leader of Scottish Labour Anas Sarwar, resorted to ranting and shouting to combat her, while new Scottish Secretary Alistair Carmichael had a torrid time in his recent encounter with Ms Sturgeon.

She is vastly experienced politically for someone aged just 43. At 34 she was already Holyrood Opposition leader, facing Jack McConnell at FMQs. As Deputy First Minister in minority government she held down the challenging health portfolio for the full term, and just over a year ago she traded posts with Infrastructure and Investment Secretary Alex Neil but also took on the responsibilities of Bruce Crawford to take on the Parliament and Government Strategy brief. No wonder it is easier to shorten all that to Yes Minister.

We met well into the evening in the still bustling suite of ministerial offices at Holyrood to talk about the recently published White Paper — all 670 pages and 170,000 words of it — and the prospects for the referendum next September.

Did a document this weighty not risk scaring off the punters? Ms Sturgeon thought not: "Actually, I'm pretty happy with the balance we struck. There is a huge appetite out there for information, for answers to questions, about a vision for things we can do if we are independent.

"So I think it was really important that the White Paper covered all of that ground, and it does cover all of that ground. It gives you this big picture, the case for independence - the democratic case, the social case, the economic case.

"It's got a wealth of detail on the affordability of independence. It gives some very practical detail about how we make the transition from a Yes vote to becoming independent and, perhaps most importantly of all, it uses some of the policy choices that we would make to start to illustrate to people what we could do with the powers of independence. Childcare was a key example of that."

She pauses then adds: "And then, it answered 650 questions. These were questions we've had submitted to us over a number of months either from organisations or from individuals. I think it was really important to bring together in one place the case for independence, how it could help us transform Scotland, and to answer the questions people have.

"I have been struck since we published it by the number of folk who are desperate to get their hands on it."

Even the full version? "Especially the full version. There is a 40-page summary document but people don't want that. They want the full one. It's been going like hotcakes. We're already into the second reprint and I have no doubt we are going to have to print more. We're number one in the Amazon free download chart."

She said that on the website or in ebook format it was fully searchable. "It's meant to be a document that if you want it in its entirety, for the long read, you can have it or can go and find anything. It's almost like an encyclopaedic resource that gives you answers to any particular questions you want."

She added: "I was at a meeting in Livingston last night - two to three hundred people at a public meeting with a lot of genuinely undecided folk - and a number of people who asked me a question referenced the question to something in the White Paper. Now, I am not saying all of them had read it from beginning to end but they had engaged with it, so I think it was really important to put that out there. It is potentially - not in one day or one week but over a period of time - going to seriously change the debate."

She then becomes unusually exercised, tapping the table for emphasis: "As things stand right now, it is the only plan for the future of Scotland. There's nothing on the other side which matches it and I think that is going to become an increasing problem for the other side. You can't get through an entire campaign just saying: 'You cannae do that!', and with ever more hysterical and incredible fears and smears.

"We're going to have the No campaign making ridiculous arguments and people are going to have to judge whether they stack up or not and I think we are reaching a stage in this campaign where they will say: 'These are the people who say you can't use the pound, your mobile phone bill will go up and you cannae watch Dr Who'.

"I just think folk are seeing through it and folk are starting to think about this in a common sense, rational way."

The indignation fades, she pauses and adds: "The other thing I detect, and it's why I think things like childcare are so important, is that people increasingly want this to be a debate about the possibilities of independence. We've set out what Scotland could look like if we were independent. I think the other side have an obligation to do the same, and are going to come under increasing pressure to answer questions about what Scotland would look like if we are not independent."

AND then the indignation begins to roll again: "What powers, actually, would we get? How do you guarantee them? Would there be further cuts to Scotland's budget? What happens if Scotland votes to stay in the European Union and the UK as a whole votes to get out? And how many more kids are going to be living in poverty by the end of this decade if we continue on the path we're on just now?

"How do we get the economy growing at a rate that matches some of our comparable countries? How do we close the equality gap if we're not independent? These are all serious questions and it's not just me saying they've got to answer them.

"Out and about I talk to a lot of folk about independence. I detect that increasingly the debate is moving into a space where people do want to compare and contrast the competing visions of the future. We've put ours out there in great detail, and there ain't nothing on the other side."

At moments like this you are glad you're not in a televised debate with her, but I venture that it was surely embarrassing recently to rely on a letter from a party activist over EU membership. She responds: "We have a position from the Commission that says they will only give a formal legal opinion if they are asked for it by a member state. The member state is the UK. We have asked them to do that.

"The First Minister said in the Chamber last week and will keep saying it: 'I will go to Brussels with Alistair Carmichael or whoever from the UK Government that wants next week and we'll ask them to give us the official European position.'. So they can't have it both ways. They can't shout uncertainty all the time when they are the ones creating the uncertainty. Well, they can choose to do that if they want. All I am saying is that people are starting to lose patience with that."

But isn't it reasonable to cast doubt on the terms of Scottish membership such as the rebate, opt-outs, the travel zone? "We are arguing in legal parlance for continuity of effect. Now if Scotland was going into this scenario saying we want to renegotiate the whole terms of our membership and having some kind of special deal, then OK, that might be a different scenario. But we're not. We're saying that the terms Scotland is currently in the EU on, in terms of the Euro, Schengen, and so on, we just want to continue."

I suggest she is arguing legally, when the real issue is political. She can't know whether Spain might choose to exercise its veto for its own political reasons. "The point at which law and politics come together on the European question is around the fact that there is no provision. People who say, whether it's Barroso or whoever, that if Scotland votes Yes it puts itself outside ... point me to the European treaty clause which says that. There is no provision to expel European citizens and we are all European citizens. There is nothing in the massive body of European law that would allow that to happen."

So you are asking us to believe the First Minister and Deputy First Minister of Scotland but not the President of the European Commission? "It's not actually a decision for the President of the European Commission. I am not asking people to believe anybody over anybody else. I am asking them to believe in their own common sense and to ask: 'What is the overwhelmingly likely outcome here?'. And I am also asking them to factor in the fact that if you vote No there is a huge question over European membership."

She makes a similar case on sharing the pound. "If we were arguing for something on the pound that was against the interest of another sovereign nation, the argument would be different. But this is a sovereign nation (the rest of the UK) that exports more to Scotland than to Brazil, South Africa, a whole host of countries put together, which exports more to Scotland than any country outside the USA.

"We are expected to believe it would say to its own business base: 'We know it would suit you to stay in a single currency with Scotland, we know Scotland wants to stay in a single currency but just to cut off our noses to spite our faces we're going to force something different on you.'. Now, is that credible? I just don't think it is at all."

But whatever the strength of argument, there are things that cannot be guaranteed — EU membership, a shared currency, access to the BBC. "That's like saying I can't guarantee the sun coming up tomorrow morning but I'm damn sure it will. The other side can't guarantee we'll be in Europe if we vote No. We are putting forward a robust, solid, common sense, reasonable, rational case."

Rejecting the suggestion that the Yes Campaign was still struggling in the polls, she says: "The latest TNS poll shows that the No vote has come down by 9%. I think we are going through a process of people starting moving away from No into the undecided category. Last October No was at 53%. Yesterday was 42% - they've lost a fifth of their support in that period.

"I am not suggesting that means we've sealed the deal but, on that direction of travel, the only movement in this debate there has been in the last few months has been away from No to undecided and our job is now to take it from undecided to Yes. You don't hear out there people saying they have gone from Yes to No. You do hear a lot of people going from No to undecided."

What did she make of recent internal criticism within the No camp of Alistair Darling? "I get lots of senses, and the Darling story was one of them, with things you pick up privately, anecdotally, that there is a real jitteriness in the No campaign. They're not sure of themselves and there is a huge unhappiness on the part of Labour activists who loathe the fact that they are in an organisation with the Tories.

"So there are plenty of signs emerging that all is not well on the No side."

But you might equally take the view that you've not seen anything yet? "We've got our plans in place, we have our vision, the White Paper is there. We're up for this, absolutely up for it. There is a confidence and an optimism and a determination on the part of the Yes campaign to take us into 2014 in pretty strong shape."

I ask about her recent suggestion that if there was a No vote there could be another referendum within 15 years — isn't that the politics of the "Neverendum"?

"That was a jokey comment about defining a generation in politics. It was not a literal suggestion that there would be another referendum in 2029. What we are saying is that next September is the only guaranteed opportunity for Scots to seize the opportunity of independence."

She adds, with an intriguing hint at a life beyond politics: "I cannot bind any future Scottish Government. I might not be - indeed there is a high probability that I will not be - in Government in 15 years' time."