Theresa May has a reputation as a cautious and even robotic speaker. But a study that analysed speeches by world leaders has found that the British prime minister can be as populist – in her rhetoric at least – as Donald Trump, Brazil’s Jair Bolsonaro and Hungary’s Viktor Orbán.

May’s public speeches were classified on average as at least “somewhat populist” in the research, which examined the discourse of prime ministers and presidents of all the major countries in Europe and the Americas in the last two decades. That made May the second-most populist female leader out of 138 heads of government since the turn of the century.

The academic study, commissioned by the Guardian, involved close analysis of the speeches of leaders who have served 40 countries to ascertain levels of populist discourse.

Quick guide The Global Populism Database Show Hide What is the Global Populism Database? The Global Populism Database is the most up-to-date, comprehensive and reliable database of populist discourse in the world. It was commissioned by the Guardian and built by Team Populism, a global network of scholars dedicated to the scientific study of the causes and consequences of populism. How was it compiled? Researchers combed through 720 speeches given by 140 government leaders in 40 countries over the past 20 years, and "scored" each based on the extent to which they used populist rhetoric. They were thus able to chart how populist various leaders were over the years. Which countries were included? The 40 countries include the eight most populous countries in the Americas: United States, Brazil, Mexico, Colombia, Argentina, Canada, Peru and Venezuela, and the seven largest European countries: Russia, Germany, Turkey, the UK, France, Italy and Spain. What were the conclusions? The study suggested that the number of populist leaders globally has doubled over the past 20 years, and that populist rhetoric - on left and right - has surged. Scholars generally agree that the central facet of populism is the use of a rhetoric that frames politics as a struggle between the virtuous will of the common people and an evil, conspiring elite.

The surprising finding in relation to May is partly explained by Brexit, the issue that has defined her premiership and dominated the UK’s political conversations since the referendum to leave the European Union in 2016.

Researchers identified several examples where May offered a romanticised description of “ordinary working people” pitted against a self-serving elite, a defining feature of populism.

Much of that rhetoric related to the UK’s vote to leave the EU in 2016, which May has called a “quiet revolution” by “the people” to “defy the establishment”. She has repeatedly spoken of delivering “the will of the people”.

Facebook Twitter Pinterest May delivering a speech on the final day of the annual Conservative party conference in Birmingham in October 2016, which was found to be arch-populist. Composite: The Guardian Design Team

Chris Wilkins, a former director of strategy at Downing Street who co-wrote the prime minister’s 2016 conference speech, which the study identified as particularly populist, said the label was fair.

“I accept that there was that theme to it,” he said of the speech given less than four months after the referendum. “That was very much the spirit of the time.”

However, he stressed May also had long-held concerns that the political establishment and the business elite had failed the country.

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The research was conducted by Team Populism, an international group of leading populism scholars who were commissioned by the Guardian to “score” the speeches of 138 world leaders. The score was arrived at through textual analysis of at least four speeches per leader, enabling an assessment of their overall use of populist rhetoric.

Tony Blair, Gordon Brown and David Cameron all had very low scores on the populism scale for all their speeches. May’s speeches, in contrast, showed more variation: two contained little populist rhetoric, while one – from the 2017 general election – contained minimal levels of populist discourse.

However, May’s fourth speech, the address to the Conservative party conference in October 2016, was evaluated as arch-populist.

The speech, written by Wilkins along with May’s then joint chief of staff Nick Timothy, described the narrow vote to leave the EU as a decisive “revolution” in which millions “stood up and said they were not prepared to be ignored any more”.

“It was about a sense – deep, profound and, let’s face it, often justified – that many people have today that the world works well for a privileged few but not for them,” May said in the speech. “The roots of the revolution run deep. Because it wasn’t the wealthy who made the biggest sacrifices after the financial crash, but ordinary, working-class families.”

She painted a picture of an out-of-touch class of politicians and commentators dismissive of the interests of regular people. “They find your patriotism distasteful, your concerns about immigration parochial, your views about crime illiberal, your attachment to your job security inconvenient,” she told her audience of Tory activists. “They find the fact that more than 17 million voters decided to leave the European Union simply bewildering.”

Those and other lines were considered sufficiently populist to give May an average score, across all four speeches, that nudged her into the lower end of a league of politicians the researchers described as “somewhat populist”. In addition to Trump, Bolsonaro and Orbán, other members of the club include India’s prime minister Narendra Modi and Italy’s former prime minister Silvio Berlusconi.

Outside of Italy, which has a history of electing rightwing populist leaders, no other western European leader scored as highly for populism in their speeches as May. The only female leader to score higher than May was Beata Szydło, who served as prime minister for Poland’s far-right Law and Justice party.

The researchers conceded that May’s score may have been swayed by one unusually populist speech.

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One of the most talked-about lines in the speech was one in which the prime minister attacked “people in positions of power” who she said “behave as though they have more in common with international elites than with the people down the road, the people they employ, the people they pass in the street. But if you believe you’re a citizen of the world, you’re a citizen of nowhere. You don’t understand what the very word citizenship means.”

Wilkins said he regretted that line “massively” because it resulted in the speech being widely regarded as divisive. The anti-elitist “citizens of nowhere” jibe, he said, had been intended as a swipe at the retail magnate Sir Philip Green. “We didn’t want to name Philip Green. But it was an attack on people who basically sunned themselves on yachts in the Mediterranean whilst their pensions funds went bust. It was actually an attempt to say the Conservative party does have a social conscience.”

Tim Bale, a professor of politics at Queen Mary University of London, who wasnot involved in the research, said describing the narrow referendum result as “the will of the people” was a typical feature of May’s populist discourse. But he stressed that plenty of Tory leaders before May had flirted with populist ideas.

“There’s always been a strong strain of populism, particularly when it comes to immigration, among Tory politicians,” Bale said, noting that William Hague, Iain Duncan Smith and Michael Howard “primed” voters for the kind of anti-elitist rhetoric that fuelled the rise of Ukip by fomenting the view that “ordinary people” were being betrayed over immigration.

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“The way it was framed was always essentially populist: ‘You, the people out there, have a common sense and completely legitimate view about immigration. The political class, the chattering classes, the liberal metropolitan elite who dominate New Labour are ignoring you and selling you down the river.”