The pro-UK Better Together campaign must set out in detail what a No vote in the independence referendum would mean for Scotland, according to Deputy First Minister Nicola Sturgeon.

The Scottish Government has provided ``a compelling case for independence'' in its Scotland's Future white paper, and unionists must respond with a competing vision, Ms Sturgeon will say in a speech at St Andrews University today.

The speech has been described as the ``curtain-raiser'' to the 2014 independence campaign as the referendum approaches on September 18.

Speaking ahead of the St Andrews address, Ms Sturgeon said: ``The referendum is not a choice between change and no change.

``It is about choosing the kind of change we want for Scotland and who we want to be in the driving seat of it - ourselves, or Westminster.

``It is a choice between two futures.

``That means that the consequences of both a Yes vote and No vote need to be considered carefully. And that means both the Yes and the No campaigns have an obligation to inform.

``Those of us on the Yes side take that responsibility seriously. In November, the Scottish Government published the independence white paper, Scotland's Future, setting out the practicalities and opportunities of what will happen if Scotland votes Yes.

``I believe it sets out a compelling case for independence. It gives robust, credible and common sense answers to the legitimate questions that people have.

``I am happy to let you - the Scottish people - be the judge of it.

``But to make an informed choice between these two futures, you also need to know what a No vote will mean for Scotland.

``Now, as we enter this next, vital phase of the campaign, it is time for the No campaign to spell that out in detail to allow you to compare and contrast the competing visions for the future of Scotland and make your own minds up.''

Meanwhile, a stronger Scottish Parliament within the United Kingdom remains the most favoured option among Scots ahead of the independence referendum, according to a poll.

Some 32% of Scottish adults want devolution inside the UK but with more powers for the Scottish Parliament, a YouGov poll on behalf of the pro-UK Better Together campaign found.

Scottish independence was the second most popular constitutional option at 30%, with the status quo of devolution as it stands today a close third at 29%.

With a total of 61% backing devolution, Better Together said the poll confirms that it remains ``the settled will of the Scottish people'', 25 years after former Labour leader John Smith first coined the phrase while laying the groundwork for devolution in 1989.

Support for independence was strongest among SNP supporters at 58% while a quarter backed stronger devolution and a tenth backed the status quo.

Better Together director Blair McDougall said: ``This poll confirms that devolution for Scotland within the UK remains the settled will of the Scottish people.

``The choice we face in September is between continuing the success of devolution as part of the wider UK or giving up on devolution and going it alone.

``Devolution has been a success and new tax-raising and borrowing powers are being delivered for our parliament.

``The three pro-devolution parties are committed to strengthening and continuing the success of the Scottish Parliament.

``Even the SNP, after a vote to remain in the UK, will have to become a pro-devolution party. It is clear there is already strong support amongst theirown voters for devolution.

``Our argument this year will be that devolution gives us the best of both worlds and this poll confirms most people in Scotland agree with us.''

A Yes Scotland spokesman said: 'What this survey shows is that most people want decisions about Scotland to be made in Scotland, and the only way to guarantee that is with a Yes vote in September.

``There is no option for 'more powers' on the ballot paper because the No parties refused to have that included.

``The poll also confirms that independence is a more popular choice than sticking with the way things are and a broken Westminster system that not only isn't working for Scotland but, as we also know from hitherto confidential government documents released in the last few days, has secretly acted against the interests and demands of the Scottish people.

``The truth is that governments at Westminster simply cannot be trusted to deliver for Scotland.''

Support for a stronger devolved parliament, often described as devo plus or devo max depending on the extent of the powers, has remained high in Scotland, leading to suggestions that the Scottish Government could include it as a third option in the referendum.

This was closed down by the Edinburgh Agreement, which stipulated that the ballot must have a single yes/no question, but all unionist parties have since declared that they would consider handing more powers to Scotland if it agrees to stay in the UK.

Deputy First Minister Nicola Sturgeon will today call on unionists to set out in detail what a No vote in the referendum would mean for Scotland during a speech in St Andrews.

The SNP said the poll had ``backfired'' on the Better Together campaign after it showed independence is more popular than the status quo.

Linda Fabiani MSP said: ``What an embarrassing start to the year for the No campaign as their own poll boomerangs.

``The No campaign has bizarrely asked questions on more powers for the parliament that they themselves blocked from the ballot paper. This poll is an absolute embarrassment.

``The reality is that this poll is consistent with a previous YouGov poll for the SNP that showed people want the Scottish Government to have powers over welfare, tax and pensions.

``But we know from history - and the latest revelations published this week - that Westminster parties can't be trusted to deliver any more powers at all for Scotland.''