The Scottish independence referendum will be a "race to the wire", the man leading the fight to keep the United Kingdom together has conceded.
With two weeks of campaigning to go until the historic vote, Better Together leader Alistair Darling said he was "absolutely confident'' that Scots will reject independence at the ballot box.
The former chancellor spoke out after it was reported a source in his campaign team had conceded they could lose the September 18 referendum.
Scotland's Deputy First Minister Nicola Sturgeon said: "There's no doubt there's a spring in the step of the Yes campaign, we're feeling very up, very optimistic.''
She added: "'The word I keep hearing over the last few days, which I think just again speaks to something in Scotland, is 'exciting'. People feel excited by what we might be standing on the brink of.''
Ms Sturgeon spoke out as she campaigned in the West Lothian town of Bathgate, where she was trying to persuade Labour supporters to vote Yes.
First Minister Alex Salmond has already said that "hundreds of thousands" of people who have previously voted Labour could back independence in the referendum.
''The evidence is Labour supporters are moving in significant numbers to Yes," Ms Sturgeon said.
''Labour supporters believe in social justice. They want to protect public services, they want to ensure that we've got a social security system that protects the most vulnerable and the best way to get these things is to put Scotland in control of our own resources and the decision that shape the kind of country we are.''
A YouGov poll earlier this week suggested support for independence had risen by eight points in a month, with the survey finding that, when undecided voters were excluded, 53% of those questioned planned to vote No while 47% would back Yes.
But Mr Darling, who was visiting Aberdeen, said: "In every single poll there's ever been we've been ahead, there are more people in Scotland that are saying No Thanks to independence.''
The Labour MP said after more than two years of campaigning the "finishing line" was now in sight, and declared: "'I'm growing in confidence that we will win, but people need to turn out and vote.'
''We will win, I am absolutely confident about that. But I have always said that it is going to be closer than people think, and it will be a race to the wire in a couple of weeks.''
Mr Darling was in Aberdeen for a business breakfast organised by industry body Oil and Gas UK, which was also addressed by Scottish Energy Minister Fergus Ewing.
He hinted that the North Sea oil industry could benefit from new tax breaks if the SNP comes to power in an independent Scotland.
Mr Ewing said it was ''crystal clear'' that if changes to the tax regime were not made, the hunt for oil would move to other parts of the world where extracting it would be cheaper.
He argued that that ''in order to maximise the economic recovery, future governments will require to play their part in considering what role tax changes are necessary to play in maximising economic recovery''.
But three Conservative former Scottish Secretaries united to release a statement which claimed the economic and financial case for Scotland breaking away from the UK was ''unarguable''.
Lord Lang of Monckton, Sir Malcolm Rifkind and Lord Forsyth of Drumlean said they believe that the ''value and the emotional appeal of the present union is far more compelling than the mirage of independence''.
A statement from the three veteran Conservatives said: ''From our knowledge gained in government, we maintain that the economic and financial case against breaking up the United Kingdom is so clear as to be unarguable; that any hope that with independence Scotland could achieve material or social objectives unavailable within the union is vain; and that the chance of Scotland maintaining in isolation the wealth and strength she enjoys as part of Britain is non-existent.''
It continued: ''We hold that the constitutional, financial and legal difficulties of unscrambling so integrated and successful a union as ours would be as complicated, damaging and heart-rending as breaking up any marriage can be.
''Divorce is always painful - the more so when the two parties must continue to live next door to one another."
Mr Salmond was in good spirits as he visited a bakery in Kilmarnock, East Ayrshire.
He was shown Brownings' specially made Aye cakes and Mr Salmond even held two of the cakes up in front of his own eyes as he continued the campaign to encourage a Yes vote in the referendum.
Despite an increase in support in recent polls Mr Salmond said the Yes campaign was still the underdog and will not become complacent.
"The strength of the Yes campaign is that it's a community campaign based on trying to do our best for the future of Scotland and that sort of grassroots campaign doesn't get complacent, they get encouraged and galvanised," the First Minister said.
"We know things are moving in our direction but we also know that we're still behind, we're still the underdogs, we've still got work to do so we're trying harder to convince our fellow citizens that independence offers a more prosperous economy but also offers, crucially, a more just society."