“Make America great again.” “Take back control.” “The people have had enough of experts.” What’s striking about the slogans adopted by Trump in the US and the Leave campaign in Britain is that they flatter the movement’s supporters as much as its leaders. They imply that the people are invariably smarter than anyone disagreeing with them, that they deserve to be in charge, that their natural greatness is being unfairly suppressed.

And whether deliberately or not, it’s a siren call to what’s known as collective narcissism, or an exaggerated love not of oneself but of one’s group. Collective narcissists aren’t personally grandiose – if anything they may feel individually powerless – but can be cultlike in their devotion to a national, religious or ideological identity with which they identify.

“Collective narcissists feel their group is threatened all the time, that others are after it. They’re prone to conspiratorial thinking,” explains Golec de Zavala, who specialises in researching the phenomenon. “Whenever they feel their group status is threatened, if they had it in their power, they would aggress against those who threaten it. Things that other people would not even notice or imagine are insulting, they would be hostile towards.”

On social media, de Zavala says, they tend to come across as “zealous” and persevere with arguments well after others have given up.