Ruth Davidson opposed the Vow, promised to Scotland during the 2014 referendum campaign but was overruled by Westminster leaders who insisted that it was made.

According to a new biography of the Scottish Conservative leader, Ms Davidson was “f***ing furious” when the plan for the Vow was drawn up by party leaders in London but her objections were not heeded.

Instead David Cameron, then the prime minister, Nick Clegg, the Liberal Democrat leader, and Ed Miliband, the Labour leader, signed up to a promise to deliver new powers for Scotland if Scots voted No in the referendum. They made the Vow, as it became known, on the front page of the Daily Record on September 16, 2014, two days before the independence vote.

Andrew Liddle,