The Scottish Government has been challenged to be "straight with the people" when ministers set out the case for leaving the UK in the white paper on independence.

Scottish Secretary Michael Moore demanded the paper - due to be published this autumn - makes clear that key areas such as Scotland's continued ability to use the pound and its membership of the European Union (EU) are subject to negotiation.

He issued the challenge to SNP ministers as he accused Alex Salmond's administration of downplaying the "fundamental" change that independence would bring.

The Scottish First Minister has already claimed a number of unions between north and south of the border would continue if there was a Yes vote in the independence referendum, saying Scots would retain both sterling and the Queen, and that the "social union" between Scotland and England would be unchanged.

Only the political union between Scotland and the rest of the UK will end if the country voted for independence, the SNP has argued.

''The social union - the ties of family and friendship connecting the people of these islands - will endure, regardless of the choices of governments,'' Mr Salmond said today.

''An independent Scotland will also retain the monarchy. Her Majesty will remain Queen of Scots, just as she is Queen of 16 other independent nations throughout the Commonwealth.

''But just because some things stay the same, that doesn't mean that nothing changes. Independence gives us the power to choose - we can choose to renew, recast and improve arrangements which no longer work for us."

However, Mr Moore claimed: "When it comes to their rhetoric about an independent Scotland, the SNP has retreated a long way in a short time.

"They no longer want to talk about how different things would be. The want us to believe instead that so much could stay the same."

With polls so far failing to show a majority support for independence, the Scottish Secretary claimed: "Having looked at the numbers, the SNP leadership has come to fear that independence is a product that too few Scots are willing to buy.

"So, to sell the goods, they are changing the packaging."

The UK Government minister, giving a speech at Glasgow University, accused the Nationalists of attempting to "de-risk independence", adding they would "pretty well say anything, do anything, promise anything to try and win" the referendum, to be held on September 18 next year.

"They are trying to de-risk, deflect and distract from the challenges and realities that would face an independent Scotland," Mr Moore said.

He insisted key areas where the position in an independent Scotland would be subject to negotiation - such as EU membership and using the pound in a "sterling zone" with the rest of the UK - should be reflected in the white paper.

Mr Moore said: "Where an independent Scotland would have the power to determine policies and priorities of its own, they should say what those would be. And where Scotland would need instead to negotiate with others, they should set out what they would hope to achieve."

He stressed that "of course the white paper cannot tell us what the outcome of international negotiations would be, nor the outcome of the negotiations that would be required with the rest of the UK".

Speaking afterwards, he added: "People have high expectations of this white paper, because it's been pointed at for months as the answer to all the questions.

"But it has to be straight with the people of Scotland about what it can be about and what it isn't.

"It can be about shaping things like welfare, but it also has to be straight about the uncertainties and the risks attacked to the negotiations, particularly on the international front.

"There's no hint on how they would square the contradictions about Nato membership or the continuing confusion over the membership of the European Union.

"This white paper has got to be substantive but it's also got to be realistic, we're expecting that when it is published some time this autumn."

With just over a year to go to the referendum, Mr Moore said the country was at a "key moment" in the debate about its future.

"It is going to be a big year for Scotland," he stated.

"In just over 12 months we will be asked to make the most important collective decision ever.

"Here in Scotland, together, we will choose between remaining part of the United Kingdom or leaving and going it alone."

Mr Moore said that was a "fundamental choice", adding: "The outcome will be either an irreversible step to a new state or the continued development of our relationship with the rest of the UK family."

He stressed the need for Scots to make an informed choice "on the basis of the evidence as well as emotion, on the basis of fact and not fiction" when they go to ballot box next September.

But he said the Nationalists "will not confirm what currency an independent Scotland would ultimately use" and "cannot tell us the terms on which EU membership might be achieved".

"Of course there are uncertainties - that is the nature of splitting up a country and starting anew," he said. "And where these exist, the Nationalists should have the courage to say so."

In his speech in Campbeltown, Argyll and Bute, Mr Salmond claimed that "independence offers the opportunity for Scotland to move away from that outdated and profoundly undemocratic Westminster system" which he said had for two-thirds of his life delivered governments with no popular mandate north of the border.

"'We will move instead to a more transparent, democratic and effective system of government - a government of the people, by the people and for the people of Scotland," he added.

With the Scottish Government proposing an independent Scotland would have a written constitution, Mr Salmond pointed out: "The United Kingdom calls itself a constitutional monarchy. But it's the only country in the European Union which doesn't have a written constitution.

''In the entire Commonwealth - even including countries which took their parliamentary system from the United Kingdom - we are the only nation without a written constitution or Constitution Act.''

He added that the process of drawing up a constitution would "energise and inspire people", adding: "It will provide us with a chance to reflect on the democracy and society we want to live in, the values that we most cherish."

The First Minister went on: "'Modern countries use their constitutions to articulate their values, to define who they are. They don't only protect human rights, they enhance liberties and define responsibilities. Scotland's constitution will do the same.

''It will make clear that it will uphold the values, rights and responsibilities of the people, of the community of the realm of Scotland. By doing so, it will make a real difference to people's lives.

''In all of this, we will adhere to one fundamental principle. In Scotland, the people are sovereign. Not the government, not the parliament, not even the monarch, but the people."