Almost half of the adults in 12 European countries now hold anti-immigrant, nationalist views, according to major new research that reveals the spread of fringe political views into the mainstream.

BuzzFeed News has been given exclusive access to new data from YouGov, which polled more than 12,000 people across the continent to measure the extent of what it termed “authoritarian populist” opinions – a combination of anti-immigration sentiments, strong foreign policy views, and opposition to human rights laws, EU institutions, and European integration policies.

The YouGov findings are the first to capture the political attitudes that are both fuelling, and being fuelled by, upheaval across Europe and beyond – from the continent's refugee crisis and the Brexit vote in Britain, to the burkini ban in France, to the rise of Donald Trump and the radical “alternative right” in the US.

In Britain, the poll found authoritarian populist attitudes were shared by 48% of adults, despite less than 20% of the population identifying itself as right-wing. Three months on from the EU referendum, prime minister Theresa May has responded this week by appealing directly to disaffected working-class voters with a promise to crackdown on immigration and reassert British sovereignty.

In France, a clear majority of people surveyed – 63% – held authoritarian populist views, while in Italy the figure was 47%. In Germany, it was 18%, which appears low by comparison but, given the country’s history and the extreme nature of its far-right groups, is regarded by analysts as surprisingly high.

The highest levels of authoritarian populist views were recorded in Romania and Poland, where they were held by 82% and 78% of adults respectively. In Lithuania, by contrast, the poll did not did not detect any evidence of the authoritarian populist phenomenon at all.