Latest indyref poll, one year to go: Yes 31, No 59, Don't Know 10

Among those who are certain to vote and have definitely decided how they will vote, the No vote continues to lead the Yes vote by two to one (67-33%). In the undecided ranks, 35% are inclined to vote Yes, while 31% are inclined to vote No.

The poll, for STV News, was carried out by phone among 1000 adults between September 9-15.

Attitudes towards independence tended to follow broad party lines. Some 68% of SNP supporters intend to vote Yes, while 75% from Labour, 80% of Liberal Democrats and 98% of Conservative supporters intend to vote No. However, the proportion of SNP supporters intending to vote Yes has fallen by eight percentage points, from 76% in June 2012, while the proportion of Labour voters intending to vote Yes has increased by a similar margin to 16%.

There are also clear differences by gender and levels of wealth. Men are considerably more likely than women to vote Yes (40-24%), while women are more likely to vote No (64-54%).

Those living in the most deprived areas are almost twice as likely as those living in the most affluent areas to vote Yes (42-22%), while those living in the latter are more likely to vote No (69-45%).

Christopher McLean, senior researcher at Ipsos Mori Scotland said: "Our latest poll suggests that neither side is currently able to shift public opinion. It is clear that the Scots who remain undecided will become increasingly important as we enter the final year.

"On the one hand, although the No vote retains a healthy lead, the Better Together campaign will need to do more to win over undecided voters if it is to win convincingly. On the other hand, with the Yes vote sticking around its historical average, Yes Scotland will need to do more to win over undecided voters if it is to gain the momentum needed to secure independence."

Tonight's poll followed three others published earlier today which were broadly favourable to those resisting independence.

An exclusive TNS BRMB survey for The Herald showed 45% of voters believe the economy would perform worse if the country split from the UK, compared with 23% who said it would improve. A further 15% believed the economy would perform the same in an independent Scotland, while 17% were unsure.

A YouGov poll for The Times found that half of people want to remain in the Union (52%), a third are opting for independence (32%), around one in seven do not know (13%), and 2% will not vote.

And a third poll by Progressive Scottish Opinion for the Daily Mail suggested that support for independence is at 27%, while 59% would vote No and 14% do not know.

At Holyrood, Alex Salmond declared independence is a "common sense position" that will be claimed by voters in the referendum next year.

The First Minister, speaking in a debate exactly one year from the historic ballot, said independence is the best route to a more prosperous country.

"This Government's argument - our most important contention - is that the people who live and work in Scotland are the people who are most likely to make the right choices for Scotland," he said at the Scottish Parliament.

"It is not an argument that is subject to statistical manipulation, it is not an argument for a day's headlines, it is not an argument born of fear. It is a common sense position based on experience.

"We have been on a constitutional journey in Scotland for more than a century. It has taken many forms as progressively we have moved forward as a country."

A Yes vote in September next year is an extension of steps towards more devolved power at Holyrood, he suggested.

"Twice before the matter has been put to a referendum and twice the people have voted in favour - once narrowly and once decisively," he said.

"The essence of that assent has been based on people expressing confidence on the ability of this ancient nation to take decisions for itself.

"That is why independence is the best route to becoming a more prosperous country but also a more just society. And that is why - exactly a year from today - the people of Scotland will claim that opportunity with both hands."

Mr Salmond said both sides of the campaign, from Yes Scotland to Better Together, must set a high standard. Debate must be respectful but vigorous to ensure the country emerges stronger, he said.

But he immediately criticised Unionist politicians, including senior Tories George Osborne and William Hague, for their approach - first to devolution and now to independence.

Accusing them of scaremongering, he said businesses have not been put off from investing.

He also dismissed previous UK Government claims that Scots may be charged higher mobile phone bills under independence.

"They were wrong because they believed that the people of Scotland would make choices which were harmful to Scotland," he argued.

"The record of this chamber has proven the opposite."

He held up the so-called bedroom tax - opposed by most Scottish MPs - as an example of Westminster imposing unpopular policies on Scotland.

"The bedroom tax is a totemic issue now. The poll tax was a totemic issue in the 1990s. It became a symbol of why devolution was necessary.

"The UK Government is implementing the bedroom tax at the same time that it is starting to replace the Trident missile system, at an estimated lifetime cost of £100 billion.

"Instead of paying for and hosting Trident, while mitigating the effects of the bedroom tax - why don't we as a country remove Trident, abolish the bedroom tax, and get on with building a better society for ourselves?"

Scotland would be able to build on its natural resources, world class universities and "astounding" cultural heritage, he argued.

The country would gain its own voice in the United Nations (UN) and would not host nuclear weapons, he told MSPs.

Scottish Labour leader Johann Lamont attacked the nationalist position that "decisions made about Scotland in Scotland will always be better".

"That is an argument that points not only to Scotland leaving the United Kingdom, but to leaving Europe, the United Nations, and Nato too," she said, "if only Scotland can decide that no power to make decisions can rest anywhere else except Scotland, and that is a self-evident nonsense."

She added: "There is an assumption that the rest of the United Kingdom wants to deny us our rights, our potential, that Scots are more progressive, fairer and more generous.

"If only we could rule ourselves, all the ills of society would disappear. That belief that there are inevitable differences denies the need every day to reaffirm the importance of fairness and justice, respect and compassion, and insults all those radical voices right across the UK who are as concerned as we are about what is happening in the country today."

Ms Lamont argued that the SNP's belief in independence was not a response to issues such as the banking crisis, foreign wars or a Tory government at Westminster.

"It is the politics of nationalism looking for a justification," she said.

"I changed my mind in the 80s when I saw what Thatcher was doing to children I taught, but I know that Alex Salmond has been on no constitutional journey - he believed in independence 40 years ago and he believes in it today."

The Labour leader said values such as community, co-operation and solidarity were embodied by the whole of the United Kingdom. She accused the SNP of re-writing Scotland's history, stating that it is the country's history and her understanding of it that makes her "a socialist and not a nationalist".

"The great changes in our history, the steps and progress in the lives of women, of people with disabilities, of people who suffer discrimination and disadvantage, in the huge issues of the environment and justice - these issues, these changes were won despite nationalism, not because of it," she said.

"You win change, not by changing the constitutional arrangements of your country, but by winning the argument and proving you can create a better society."

Ms Lamont said a No vote next year would end the political equivalent of a "get out of jail free card" for the nationalists, and allow politicians to "start dealing with the real challenges of life in modern Scotland". She said today's SNP administration is a campaign, rather than a government.

"Let's make the case, stand up for the United Kingdom, refresh the opportunity to defeat nationalism, do the real job of politics, make and win the political case for the real change we need to make our society stronger and fairer," she said.

"Not the tired and tedious, not the old songs, but honesty openness and coming together to deal with the real experience of Scots across this country."

Scottish Conservative leader Ruth Davidson, making her case for the UK, said the British armed forces are "the most professional fighting force on the planet".

They are "in the top three defence forces around the world" in defence spending as a proportion of the economy, she told MSPs.

"We are stronger together as part of the UK armed forces," she said.

"Scots around the world, proud to serve with the Union flag on the arm of their uniform, are part of the most professional fighting force on the planet.

"Our integrated land, sea and air platforms allow us to respond to conflicts and crises in all parts of the globe and I believe the defence of our allies, our response in the world, and the safety and security of our people at home are best served there."

Veteran nationalist Margo MacDonald, a former SNP MP who now sits as an independent MSP, asked if Ms Davidson's portrayal of the British armed forces was a joke.

"There are fewer men under arms in the armed services now than at the start of the battle of Waterloo," she said.

"Recently, in response to Syria, it was reported that the American fifth fleet had moved into the Persian Gulf, the sixth fleet had moved to the eastern Mediterranean, while the British had a submarine somewhere in Cyprus. Are we joking about this great British defence?"

Ms Davidson replied: "I believe that on the imprint of our footprint around the world we are in the top three defence forces in the world, our commitment to GDP in how we fund it.

"The future alliances and security that we have is best served by a British army, navy and air force not on the division of personnel, platforms, assets and hardware.

"If Ms MacDonald is making the point that she sees that the size of our imprint is less than it once was, then breaking up our nation and defence footprint is not the point that she is trying to make."

Liberal Democrat MSP Tavish Scott said people wanted answers on issues such as employment and pensions but, on every area of policy, independence was like "a walk in the dark".

"It is opening a door into a pitch black room and trying to find the door on the other side," he said.

"We may never come out, but the one certainty is the door marked UK will be locked forever. There is no way back."

Mr Scott restated the Lib Dems' policy for a federal UK, and welcomed "progressive voices from Labour" in this area.

"This nationalist government is sadly fixated. Not on Scotland's needs, but their own," he said.

"I confess that I misjudged Mr Salmond's government. I actually thought the SNP believed in a decentralised state with decision-making involving local people in their own towns, villages and communities.

"But six years of nationalist government has shown how wrong I was. The most striking change is centralisation - the command and control of the public sector by nationalist ministers, local government removed of its financial powers, and police centralised into a national force."