Scottish Secretary Alistair Carmichael has claimed that uncertainty over a range of unanswered questions gained “traction” among the electorate in the final days of the campaign.
The MP for Orkney and Shetland said he hoped the mood of people across Scotland experienced by campaigners on the ground would be reflected in a No vote.
Mr Carmichael admitted he was excited and nervous at the same time as sources close to the Better Together campaign said they were increasingly confident the final result would go their way.
One suggested the result could be 55% for No but a senior figure in the Yes camp said it was “too early to say”.
Mr Carmichael, a Liberal Democrat MP, said: “It is the end of a two years campaigning and I have mixed emotions.
“There are elements of excitement, nervousness and all the uncertainty because there is nothing we can do to change the result now.
“We will have to wait and see what the final result is going to be.”
Mr Carmichael said it was the Scottish Government had made the case for change but had not managed to convince many voters.
“They invited a whole range of questions about currency, about the security of people’s pensions, our membership of the European Union which they then failed to answer,” he added.
“That I think really caught some traction in the final days of the campaign and I hope you will see that reflected in the results tonight.
Hundreds of people attached to the pro-independence group Yes Scotland and their rivals have packed into a massive barn at the Royal Highland Centre in Edinburgh to learn Scotland’s fate.
The atmosphere is muted and tense as campaigners on both sides of the historic debate discuss the likely outcome.
Around 500 members of the media from around the world are based in an equally large barn-type hall across a passage from the main hall where the final result is expected to be announced by chief counting officer Mary Pitcaithly at around 7am.