Ms Davidson posted on Twitter that “any Conservative leadership candidate must put the Union first – Jeremy has done so and will get my vote”. The Scottish Tory leader endorsed the Home Secretary Sajid Javid at the start of the contest, introducing him at his campaign launch. After Mr Javid was eliminated, she backed Michael Gove to become the challenger to Mr Johnson, who is widely expected to win the Tory leadership. Mr Gove and Mr Javid were the only UK ministers invited to speak at this year’s Scottish Tory conference. It is the latest sign of the hostility to a Johnson premiership among many Scottish Tories, who worry the former Foreign Secretary and Brexit campaign leader would be toxic to the party’s fortunes in Scotland. A senior party source said they were “surprised” by her third endorsement of the contest, saying it “makes it look even more like an ‘anyone but Boris’ strategy”. Last year, it was revealed that senior Scottish Tories had formed a plot to block Mr Johnson from becoming leader, dubbed ‘Operation Arse’. Polling this week reinforced claims that Mr Johnson is deeply unpopular in Scotland, with a negative approval rating worse than that of Jeremy Corbyn. Ms Davidson’s endorsement came as it was revealed that Mr Hunt had secured the support of more than half of Conservative MSPs. The Foreign Secretary has also picked up the endorsement of two Scottish Tories who had backed Mr Gove in the final ballot of MPs, Paul Masterton and Bill Grant. In a joint letter, Mr Hunt’s Scottish supporters said the party had to “choose a candidate who we can trust to unite the country”. The Scottish parliamentarians wrote: “The eventual Prime Minister must be able to deliver a good Brexit deal and, even more importantly, protect and strengthen our precious Union.” The letter goes on: “On a visit to Scotland in the first weekend of his campaign, the Foreign Secretary said that he would never do anything that would threaten the Union. When asked if he would pick the Union or Brexit, he said ‘the Union every time’. “There is no issue of greater importance to the Scottish Conservative and Unionist party than ensuring that Scotland’s place within the United Kingdom is protected and enhanced. Jeremy Hunt has proven to us that he understands Scotland’s interests and will do whatever it takes to keep Scotland in the Union.” Three of Mr Johnson’s Scottish supporters hit back, signing a letter that said “no candidate is more Unionist than the other”. Mr Hunt said: “I visited Scotland on the first weekend of my campaign to set out how I would strengthen the Union. I am delighted to have since gained the backing of so many Scottish Conservatives.” Mr Hunt has backed calls from Scottish Tories for the UK Government to take a greater role in Scotland.