Ruth Davidson was David Cameron's 'political soulmate'

Ruth Davidson has been described as a "political soulmate" by former prime minister David Cameron, who believed she would drive the party to win the most Scottish seats at Westminster.

Ruth Davidson at the press conference to announce her resignation as Scottish Conservatives leader

Writing in his new autobiography For the Record, Mr Cameron said he had been buoyed by Ms Davidson's rise as leader of the Scottish Conservatives.

"Ruth and I were immediate political soulmates.

"I was so proud of how our party had changed and excited about what we could achieve with Ruth at the helm in Scotland."

Ms Davidson resigned three weeks ago as the Scottish Tories leader, citing family commitments and her conflict over Brexit among reasons for her decision.

Mr Cameron had shown his public backing for Ms Davidson on a series of occasions, including when he used a speech at the party's 2013 conference in Stirling to reprimand those who had questioned her initial performance.

The Conservatives would go on to return 13 MPs in 2017 compared with the SNP's 35.

"With the phenomenal Ruth Davidson at the helm, I don't doubt that we could become the biggest."

An SNP spokesman said in a statement: How time flies. The Tories are in tatters, leaderless and in a head-first race to the extremes of British politics with the Brexit Party.

"If Ms Davidson can't put up with Boris Johnson, why should Scotland?"

Mr Cameron has conceded in his new book the 2014 referendum on Scottish independence was a "gamble".