“If you’re one of these families, if you’re just managing, I want to address you directly. I know you’re doing your best. The government will be driven not by the interests of the privileged few, but by yours.”

Those words, delivered by the Prime Minister in front of 10 Downing Street on the day she took office, were noticed at the time more for their arresting statement of values than for their rhetorical style. Here was a Conservative Prime Minister declaring her commitment to social justice. That, rightly, was what captured the headlines.

But there was something else going on in those sentences. It felt new, somehow, for a Prime Minister to identify a section of society and say: “I am talking to you.” This unusual rhetorical device was undoubtedly successful. It made viewers sit up and listen. But the grammar wasn’t just effective – it was unsettling, as well. It was hard to pin down why, exactly. But something about it carried the suggestion of a threat.

Last night, it all became clear. Once again Theresa May addressed the nation. But this time she delivered a stone-cold populist speech which sets her on a path towards genuinely threatening the future of our pluralist democracy.

“Of this I am absolutely sure,” the Prime Minister told us. “You the public have had enough… You want this stage of the Brexit process to be over and done with. I agree. I am on your side.”

“I am on your side” is the archetypal populist statement. For populists, politics is simple. There is the people – one unified and homogenous mass with a clearly identifiable will. Then there are the enemies of the people – sometimes wealthy elites, sometimes faceless bureaucrats, often foreigners and those who look or sound different to the majority. And finally there is the leader, who is the tribune of the people, the megaphone for their will. The leader, you see, is always on your side.

It is no coincidence that Theresa May is so fond of addressing the nation directly. In British politics, the lectern usually comes out only for genuinely seismic announcements or to mark historic moments. But in the last few months, the Prime Minister has used several addresses more to emphasise points she has already made than to announce anything. And last night was a case in point. She had made exactly the same argument in the House of Commons at midday. Since then Donald Tusk had complicated things by saying an extension would only be granted if her deal was passed. Yet she made no reference to Tusk in her speech. Why? What was the point of addressing the nation?

The answer can be found not in the politics of the moment but in the political character of the Prime Minister. Populists love to speak directly to their cherished ‘people’. It is a way of re-grounding themselves, and sidestepping the messy web of democratic institutions – Parliament, journalism, the courts and so on – which only serves to complicate the pure relationship between leader and people. In the tangle of that web, the will of the people is not always obvious. But when the leader is addressing the people directly, all that confusion melts away. That’s what last night was about. And that’s why the speech seemed so irrelevant to the real debate.

Of course, for those who identified with the Prime Minister’s words – who agree not only that it is time to get on with Brexit, but that she is being thwarted by the latest ‘enemy of the people’, Parliament itself – her speech last night may have landed well. But the problem with populism is that ‘the people’ are plural, not singular. For those who disagree with her, those words “I am on your side” may instead have sent a chill through their veins. If the Prime Minister is picking sides and you find you’re not on hers, perhaps it’s time to worry. Particularly when she’s talking directly to you.

Populism can be deeply unsettling for those who do not follow the leader. But for those explicitly identified as enemies of the people it’s downright dangerous. It comes as no surprise that several MPs responded to her speech with expressions of fear for their own and their colleagues’ safety. There can be few more chilling experiences than being singled out and targeted by a political leader. Often it is an ethnic group or migrants that are on the receiving end of populism. The fact that last night MPs were the target makes the technique no less excusable.

Some argue that populism is a necessary or useful democratic phenomenon. Margaret Canovan calls it the “shadow” of democracy – when democratic politics gets too consensual and fails to represent popular grievances, populism is a steam valve which can release the pressure in the system. Others, particularly on the left, defend populism on the basis that the only way to shift a deeply entrenched policy paradigm (neoliberalism, say) is to identify those for whom the paradigm works (‘the elite’) and construct an entity (‘the people’) to oppose it.

But what these arguments miss is the inherently dangerous aspect of populism, which is its insistence that the people must be of one mind. Democracy is sustained by the assumption that people are different. Otherwise why bother voting at all? When politicians adopt the mantle of populism – when they paint us all into a corner, and claim that the very institutions which can express our differences are in fact working against our interests ­– they are undermining democracy itself.

Our society is inherently diverse, and is strengthened immeasurably by that diversity. Any political strategy which seeks to homogenise us should always be denounced in the strongest possible terms. We should call it out for what it is: anti-democratic, and inhumane.