Ruth Davidson has issued a defiant challenge to Boris Johnson, pledging she will refuse to back a no-deal Brexit before his first visit to Scotland as prime minister.

The leader of the Scottish Conservatives is expected to meet Johnson in Edinburgh on Monday, after the prime minister begins his trip north with a visit on the west coast.

Writing in her regular column for the Scottish Mail on Sunday, Davidson said: “When I was debating against the pro-Brexit side in 2016, I don’t remember anybody saying we should crash out of the EU with no arrangements in place to help maintain the vital trade that flows uninterrupted between Britain and the European Union.

“I don’t think the government should pursue a no-deal Brexit and, if it comes to it, I won’t support it.”

Saying she had confirmed her position to Johnson when the pair spoke by telephone last week following his election as UK Conservative leader, Davidson added: “As leader of the party in Scotland, my position exists independently of government. I don’t have to sign a no-deal pledge to continue to serve.”

Davidson’s public defiance – just as the Brexit planning minister Michael Gove confirmed that the government was operating on the assumption that the UK would leave the EU without a deal on 31 October – will further test her already strained relationship with Johnson.

She was reported to be “livid” after the prime minister sacked her ally, the Scottish secretary, David Mundell, and appointed Alister Jack in his place. Mundell later confirmed that Johnson had replaced him because he “wasn’t as on board with a no-deal Brexit as [Johnson] would want me to be”.

Johnson went on to appoint an English MP, Robin Walker, as a junior minister at the Scotland Office, in an apparent snub to the 12 other Scottish Conservative MPs. Johnson later added Colin Clark, one of his most vocal supporters north of the border who unseated Alex Salmond in the 2017 general election, to the team.

This repositioning appeared to contradict assurances from Johnson allies that he is willing to take guidance from Scottish colleagues on strengthening the union.

Warning that “politics is about more than personalities”, Davidson promised that she “will not be backward in challenging Mr Johnson’s government where I think they are getting it wrong”.

She wrote: “I will work hard, be professional and build constructively on the work that has already gone on to ensure the UK government delivers for Scotland, in Scotland.”

Early in the leadership campaign, Scottish Conservative critics said a Johnson premiership would spell catastrophe for the party, boosting support for independence and bolstering Scottish nationalist arguments that Westminster represents only a wealthy, southern elite.

Davidson conceded that she was united with the new prime minister “in our determination to stop Nicola Sturgeon trying to use the differences that do exist across the UK as a pretext for breaking us apart”.

She also underlined her opposition to the creation of a separate Scottish Conservative party, which some supporters have suggested is the only way to consolidate the gains that she has achieved in Scotland against the ramifications of Johnson’s Brexit strategy.