ITV News Political Analyst Professor Colin Rallings has warned that the margin of error in recent opinion polling means the potential true figure could be anywhere between a 1% Yes lead and a 10% No win.
Three polls released last night all had the No vote ahead by 52% to 48% but include a 3% buffer.
"The pollsters themselves are very concerned about the scope for a bit of a pit opening up in front of them here," he said.
"The turnout is likely to be so high [estimates suggest up to 80%] that perhaps a third of people will never have voted before in a recent election."
This, professor Rallings explained, makes it much more difficult to predict voting patterns based on previous loyalties.
One story dominates Thursday's front pages with some newspapers printing emotive pleas to voters to keep the United Kingdom as one.
In Edinburgh tonight you can hear it and feel it. The buzz, the banter of the day and the thrilling sense something big is coming tomorrow.
There is nervousness, anxiety and on the streets of Edinburgh fuelled by an atmosphere unlike anything seen before in recent UK politics.