Britain is beginning to reassess how reliable an ally the US is, the Scottish Conservative party leader, Ruth Davidson, has said, in comments that contrast starkly with the official policy of the UK government.

During an interview at the Women in the World summit in Washington, Davidson said: “At the moment, from the UK, we have always seen America as being a very strong, a reliable ally, and now, even after only 26 days or however long [Donald Trump’s] tenure has been so far in Pennsylvania Avenue, we are beginning to reassess how reliable an ally the United States is.

“And that’s a huge change in Europe. That’s a massive, massive shock. We are going to want to make sure any deals that are done [Trump] is going to honour. We have to be sure of that.”

Theresa May was the first world leader to visit Trump after he became president and she has been clear that the relationship between the UK and the US will remain strong, despite the controversies surrounding the Trump administration. On the eve of her visit to the Oval Office in January, May told journalists that “opposites attract”.

Speaking before a press conference on Thursday in which Trump attacked the media, Davidson said the trend for politicians to demonise the media should “worry us all”.

“We have to be very careful about popular nationalists, populist strongmen, part-demagogues, using a lot of their political capital at the beginning of their journey to delegitimise public scrutiny, which is what demonising the media does,” she said.

“And I think that if we learn our lessons from history, there is a very strategic reason why you’d do that and I think that should worry us all.”

Davidson said it was only lazy members of the media who thought she was not “what you would expect a Conservative necessarily to be”.

“The idea that I’m something completely other is wrong because I worked for 10 years as a journalist for the BBC, and for others, and was interviewing politicians every day, so I wasn’t completely foreign to the world,” she said.

“It wasn’t like a bunch of one-step-away-from-white-supremacist bloggers that are living just up the street,” she added, taking a swipe at Steve Bannon, Trump’s chief strategist and the co-founder of far-right website Breitbart News. “And it turns out they’re completely chaotic.”

Davidson expressed reservations about the decision to invite Trump on a state visit to the UK. “The whole point of state visits is that it’s about having people who share your philosophy – your friends and all the rest of it. That’s the difference from a bilateral summit or whatever,” she said.

“And the thing that I had a problem with is that that could go on while there are members of my own country being banned from [the US], people with joint passports.”

But she concluded: “I will extend, and I’m sure the government of the United Kingdom will extend, every courtesy to the president of the United States when he arrives, as you should with any world leader, but we’re going to want to make sure that any deal we do he’s going to honour. We have to be sure of that.”

It is not the first time the Scottish Tory leader has been critical of Trump. Before he was elected, Davidson was reported by the Herald newspaper as saying the billionaire’s “impetuosity could be dangerous not just for America but for the world”.

A source at the Foreign Office said the official position on the UK-US relationship was well known and had not changed.

Speaking in the Commons last month, the foreign secretary, Boris Johnson, said the UK’s alliance with the US was vital. “On defence, intelligence and security, we work together more closely than any other two countries in the world. That relationship is overwhelmingly to our benefit,” he said.

“The prime minister’s highly successful visit to the White House last week underlined the strength of that transatlantic alliance. Where we have differences with the Unites States, we will not quail from expressing them.”