RUTH Davidson hated "the Vow" promising more powers for Scotland ahead of 2014’s independence referendum and was furious with her counterparts in London for pushing on with it regardless.

A new biography claims the Scottish Tory leader was “strongly opposed” to the pledge to deliver greater devolution, which was made on the front page of a tabloid newspaper in the days running up to the vote.

While supportive of more powers, she felt the move handed the SNP an open goal after the referendum to keep the narrative of independence alive.

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The Vow, which appeared on the front page of the Daily Record on September 16, 2014, two days before the independence vote, was partly blamed by former first minister Alex Salmond for losing the referendum.

It was signed by then prime minister David Cameron, his Liberal Democrat deputy Nick Clegg and Labour leader Ed Miliband, and was widely seen as a last-ditch attempt to save the union in the face of damaging polls.

But a new book by Andrew Liddle, a Scottish Labour spin doctor, claims the decision to push ahead was condemned by Ms Davidson.

In Ruth Davidson and the Resurgence of the Scottish Tories, Mr Liddle writes: “From Better Together’s point of view – with the campaign increasingly distraught at the prospect of defeat – it was probably a success, at least in the short term.

“But Ruth was – in the words of one senior party insider – ‘f**king 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.”

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Mr Liddle’s biography also quotes a senior insider, who insisted: “It was the only time [Ms Davidson] got angry during the campaign. She felt that this would allow the SNP narrative to get going again.

“So rather than us voting on independence, what we had was a scenario where the Nats would be able to turn round immediately and say we were offered this bribe of new powers and now it is not going to be delivered and x, y and z.

“She was very angry about that. There were some interesting scenes in the Better Together office.”

Former first minister Alex Salmond previously claimed the Vow was “decisive” in Better Together winning the referendum.

In the days following the vote, he said: "I think the Vow was something cooked up in desperation for the last few days of the campaign and I think everyone in Scotland now realises that."

A senior Scottish Tory source insisted Ms Davidson supported greater devolution for Scotland, with her opposition to the Vow simply about “tactics”.

But the SNP seized on the revelation to brand Ms Davidson’s commitment to devolution “about as paper-thin as the rest of her policy platform”.

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SNP MSP Ash Denham said: “Ms Davidson won the support of the Tory grassroots by telling them she’d draw a ‘line in the sand’ against any further powers, but ditched that as soon as she realised how unpopular it would be with everyone else. Now it seems that even that commitment was itself just a ploy and that she was in fact bitterly opposed to the Vow.”

Scottish Labour leader Richard Leonard said it “blows apart Ruth Davidson’s claims to be a different type of Tory”, and argued the claims proved her party could not be trusted to defend devolution.

But a spokesman for the Scottish Tories said: "What complete nonsense from Richard Leonard. It was the Scottish Conservatives who first set out plans for a more powerful Scottish Parliament before the referendum. Scottish Labour had to be dragged kicking and screaming into adopting them."