Better Together leader Alistair Darling has said he is "absolutely confident" that Scots will vote to stay in the UK but conceded the referendum campaign will be a "race to the wire".
The former chancellor said he is "increasingly confident" that voters north of the border will reject independence when the referendum is held on September 18.
He spoke out after it was reported that a source in his Better Together campaign had conceded they could lose the historic ballot.
The Herald has reported an unnamed insider as saying: "The ground has shifted a lot in the past week. I still think we'll win, but it's close and it's possible we'll lose.
"Yes can win from here; that's a shift in my thinking. I really never thought we would lose. Now I'm thinking it's possible we might."
But Mr Darling insisted: "That's rubbish, we will win."
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.
Mr Darling, who was visiting Aberdeen, said no changes would be made to the campaign as a result of such studies.
"Our campaign has been focusing on the positive advantages of being part of the United Kingdom, the opportunities, the job opportunities, as well as the security of making sure we can pay pensions," he said.
"We will continue making that case right up until September 18. It's a central part of our argument and I believe our argument will win.
"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."
With the referendum campaign having gone on for more than two years now, Mr Darling said: "The finishing line is in sight, we will win.
"I'm growing in confidence that we will win but people need to turn out and vote."
He added: "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 stated: "In the next two weeks we will decide the future of our country. If we decide to leave there is no going back. With all the risks and uncertainties, I think we should say No Thanks to that.
"We can have the best of both worlds - Scotland can and should be a better place to live, a fair and more just place, but we can do that better with the opportunities, the job opportunities, and the security through the strength of the United Kingdom."