SCOTTISH Tory boss Ruth Davidson was “f***ing furious” about The Vow, a new biography of the politician has claimed.

The promise to deliver new powers to the Scottish Parliament if Scots backed a no vote in the 2014 referendum on independence was drawn up by Gordon Brown and backed David Cameron, Nick Clegg, and Ed Miliband.

The Vow, as it became known, was printed on the front page of the Daily Record on September 16, 2014, just two days before the independence vote.

The National:

Andrew Liddle, the former Press and Journal reporter who has written the new biography, said Davidson thought that the pledge was unnecessary and would hand the initiative to the SNP after the vote.

In his book, Ruth Davidson and the Resurgence of the Scottish Tories, Liddle writes: “Ruth was – in the words of one senior party insider – ‘f***ing furious’ with Cameron over the Vow. While she had been consulted over the pledge, she was strongly opposed.

“The Scottish Tory leader – rightly – argued that the Vow would play right into the Nationalist narrative. SNP leaders would be able to suggest that they did not lose on the question of independence, but rather the vote was one about more powers.”

Liddle adds: “One senior insider, who was with Ruth when the Vow was being discussed, said: ‘It was the only time she got angry during the campaign. She felt that this would allow the SNP narrative to get going again ... There were some interesting scenes in the Better Together office.’ ”

The Vow has become a totemic issue for many on the yes side, with some firmly believing it was the promise of new powers for Holyrood that helped snatch defeat from the jaws of victory.

Though a survey of more than 4500 people in 2015 by Edinburgh and Essex universities revealed that just 3.4% of No voters said the offer of more powers was the main motivation for their decision. Rather, it was No voters’ feelings of Britishness and their doubts about the economics of breaking up the UK that led to them rejecting independence.

That was disputed by former First Minister Alex Salmond.

At the time, he said: “People, when you ask them why they did something – do not necessarily say what was actually the case.

“It is far easier for someone to say ‘oh yes, it was the economics of the currency position that really concerned me’ – as opposed to saying ‘I really got taken in by these three chancers when they came up and told me we could have all the powers we wanted if we voted No’.

“That’s quite difficult for people to say, because it accepts we were willing to be swayed by what became pretty obviously – a guise, a manoeuvre.”

The former SNP leader compared the “vow” to the case of one of his constituents who had £20,000 embezzled from him by a get-rich-quick scheme.

“It was patently obvious that this organisation, which had been taking his money ruthlessly and disgracefully, was a fraud and a racket. But I couldn’t get him [the constituent] to believe it, because [it was] the last thing he wanted to do for his own self-esteem. This was an intelligent man – in his late 70s but still an intelligent man.

“The last thing he wanted to do for his self-esteem was to accept that he had been taken in and duped – made a fool of. People find it difficult do say that.

“Far better to say ‘I made an examination of the full implications of the currency question and came up with a different answer’. That’s human nature.”

A senior Scottish Tory source confirmed the accuracy of the claims made in the book to the Times.

He said: “This is all now ancient history. But given what happened after the referendum, history might conclude Ruth had a point.

"The important thing now is that the powers contained in the Vow have been delivered as promised. Meanwhile Alex Salmond’s grievance narrative has become utterly discredited. Whatever disagreements there might have been at the time, Better Together’s work has stood the test of time.”