According to 'Call Me Dave', Lord Ashcroft and Isabel Oakeshott's explosive biography of the prime minister being serialised in the Daily Mail, Cameron lost his "calm" after the shock poll showed Yes in the lead less than two weeks from election day.
Cameron was in Scotland at the time, staying with the Queen at her Balmoral estate and she noted the headline of one the papers reporting the poll during a "strained" breakfast with him.
"One of his normal characteristics is the ability to stay completely calm when everyone is panicking. This is one of the few times he didn’t do that," an unnamed friend told the authors.
In the latest Daily Mail serialisation, pollster Andrew Cooper described Cameron phoning from his car. He said: "He was very worried... It was the first time he was seriously contemplating: “Shit, we might lose.”
The revelation follows the headline-grabbing claim in the book that Cameron put his private parts in the mouth of a dead pig in a bizarre initiation ceremony.
The book also claims the Queen's private comment just before the vote that Scots should "think very carefully about the future", which was overheard by people nearby, was actually deliberate.
The Cabinet Secretary Sir Jeremy Heywood and the Queen's Private Secretary Sir Christopher Geidt had worked out a way for the monarch to signal her view in a coded way that would not breach her neutrality according to the book.
In the end, the Scots voted no by 55% to 45% but the following months saw huge momentum gather behind the nationalist SNP, which won 56 of 59 parliamentary seats in Scotland in May.
First Minister Nicola Sturgeon has challenged the leaders of Scottish Labour and the Scottish Liberal Democrats, Kezia Dugdale and Willie Rennie to stop opposing a second independence referendum.
Both leaders oppose it but have said, if one takes place, they would allow their party members to campaign for or against it.
“It is not going to cut much ice with supporters of independence in their own parties to say in one breath, ‘You know, if there’s another referendum you can stand up for what you believe in’. But in the next breath say, ‘But we think a referendum should be ruled out forever and a day’," Ms Sturgeon said.
“My challenge to Kez and Willie is this. If opinion doesn’t significantly shift from the referendum last year – or if there is no material change in circumstances from the debate last year – it wouldn’t be right to hold a second referendum.
“So the challenge is: do they agree with me on the converse? If we do see opinion shift or if we do see a material change in circumstances, surely they must agree that it would be equally wrong for any one politician to rule out a referendum indefinitely in those circumstances.”