NEARLY half of Scots voters believe independence would harm the economy, according to a new poll which shows the scale of the task facing the Yes campaign exactly one year out from the referendum.

An exclusive survey shows 45% of voters believe the economy would perform worse if the country split from the UK, compared with 23% who said it would improve.

Faced with the key question a further 15% believed the economy would perform the same in an independent Scotland, while 17% were unsure.

The TNS BRMB survey was conducted for The Herald to coincide with the one-year-to-go landmark in the referendum battle. Voters will go the polls 365 days from today, on September 18 next year.

Read Robbie Dinwoodie's full interview with Alex Salmond

Scotland Decides: read our 20 page supplement

Tom Costley, the head of TNS ­Scotland, said the findings highlighted "a generally downbeat view about the economic prospects for an independent Scotland".

Responding to the poll, a spokesman for the pro-independence campaign Yes Scotland said: "A Yes vote puts our country's economy and its future in our own hands and that means we can choose to make Scotland's wealth and resources work better for the people living here, which will deliver higher standards of living and more opportunities for the people of Scotland.

"Of course polls will continue to show varying results between now and the referendum, but we are confident that on September 18 next year Yes will win in the only poll that really matters."

A spokesman for the pro-UK group Better Together said: "The rest of the United Kingdom is our biggest trading partner. It is only Alex Salmond and his Ministers who think that creating barriers to this trade is a good idea so it is little wonder that people are not convinced by the nationalists' arguments."

Two other polls have put the No campaign ahead in the battle to win the referendum. A YouGov poll finds 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. The poll for The Times, carried out between September 13 and 16, asked 1,139 people the question: "Should Scotland be an independent country?"

Another poll by Progressive Scottish Opinion finds that support for independence is at around one in four (27%), while three-fifths will vote No (59%) and one in seven do not know (14%). The survey, commissioned by the Daily Mail, questioned 1,051 Scottish adults last week.

The polls came as a new report from the National Institute for Economic and Social Research warned an independent Scotland could start life with debts of more than £150 billion and that it should consider an "oil for debt" swap to pay off the rest of the UK.

The referendum race enters its final 12 months more than two years after the SNP won an overall majority at Holyrood, making the historic vote possible.

The First Minister announced the date of the referendum in March. Voters will be asked the Yes/No question: "Should Scotland be an independent country?"

The Scottish Parliament will mark the milestone today with a set-piece debate.

Speaking ahead of it, Mr Salmond said: "Today marks one year to the biggest opportunity Scotland has ever had - referendums like this are a once in a generation event, which means the vote on September 18 next year will be the opportunity of a lifetime for many people in Scotland, as we get the chance to choose our country's future."

He added: "Scotland can more than afford to be a successful independent country. We have enormous advantages in terms of our human and natural resources, but we need the political and economic tools to help create a wealthier and fairer society."

Today he will join Deputy First ­Minister Nicola Sturgeon - the "Yes minister" in charge of referendum strategy - at a creche in Edinburgh as politicians on both sides use the symbolic date to step up their campaigning.

In a sign of the importance placed on the economy as a possible deciding factor in the referendum, year-to-go messages from Ms Sturgeon and Blair Jenkins, the head of Yes Scotland, also stressed Scotland's ability to thrive outside the UK.

Mr Jenkins said: "We are one of the wealthiest nations on Earth. The key question is about how we use those vast resources."

Ms Sturgeon said: "An independent Scotland, with control over all policy areas affecting people's lives, will give us the economic and political tools we need to build a more prosperous society."

The Scottish Secretary Michael Moore agreed the referendum was an "absolutely defining moment and a once-in-a-lifetime choice".

But, urging people to "think ­carefully", he added: "I firmly believe that Scotland will be stronger, more secure and more prosperous if we remain as part of the UK."

He will use his keynote speech to the Liberal Democrat conference in Glasgow this morning to claim that opting for independence in next year's referendum would mean choosing to "become less than we are now".

He will say: "We well understand that to leave the United Kingdom is to leave behind its structures, its institutions and our Britishness too.

"You cannot be of the United ­Kingdom if you are not in the United Kingdom. And Scots do not want to choose between Scottishness and Britishness; to become less than we are now. Why should we? Why must we choose just one when we can benefit from both?"

Alistair Darling, the head of Better Together, told The Herald it was in Scotland's "best interests" to remain part of the UK economy.

A number of polls are expected today. Averaging surveys out over the past year, Scots are split roughly 60/40 in favour of a No vote, not taking the don't-knows into account.

Scottish bookmakers yesterday predicted that £5 million will be wagered on the outcome of the referendum as they made a No vote the clear favourite, with odds of 1/7. A Yes vote was a 4/1 shot, they said.