"Now, what I want is facts," blasted Mr Gradgrind, the terrifying schoolmaster in Charles Dickens's novel Hard Times. "Teach these boys and girls nothing but facts."

The reader imagines a group of Victorian pupils quivering at their desks, cowed into submission by an endless diet of algebra and battle formations, their imaginations (known as "Fancies") being repressed as frivolous and sinful.

In reality, of course, the accumulation of facts doesn't have to be a bleak and miserable exercise. For the Jewish community, the art of citation has long been a joyful tradition. For the religious, this revolves around the endless analysis of Talmud. For the more secular, the Friday-night dinner table has provided a forum for vigorous analysis, discussion and argument.

In much of western Europe, the population's memories of the facts of the recent past have guaranteed mainly moderate political leaders since the end of the Second World War and safety for minorities, including the Jews.

Yet something quite weird is happening. Over the past few months, facts have gone out of fashion. The rules of the game are changing as, propelled by the power of celebrity and social media, we gradually enter a post-factual age.

In Donald Trump's speech to the Republican convention, he made a quite extraordinary pledge, to end all crime. Or, in his own words, to "stop the gangs" and "stop the violence". It doesn't compare to his other jaw-dropping pronouncements, including this week's lamentable spat with the family of an Islamic-American war hero but it still drew raucous whoops from the crowd. Trump could easily become President.

In Britain, too, politics has been pushed into the realms of fantasy. The central Vote Leave campaign pledge, that exiting the EU would see £350m per week handed to the NHS, was largely plucked from the sky and within hours of the result, disowned by those who proposed it. The man who helped to think it up is now foreign secretary.

At the other end of the political scale, Jeremy Corbyn's most powerful trade union supporter recently claimed that the Labour leader's opponents are really secret MI5 agents.

In my newspaper, The Times, Robert Harris compared Britain today to Munich in 1938. Power, he says, is in danger of leaving the realm of the parliamentary chamber, and being transferred to the mob . "At any given time there's always a percentage of the population that's psychopathic and the important thing is to keep their hands away from the levers of power," he wrote. Yet, as the Establishment is portrayed as increasingly corrupt, the pledges of those in positions of authority fall on deaf ears. To coin Michael Gove's phrase during the referendum: "People in this country have had enough of experts."

Those in populist movements, rapidly gaining ground in their world full of resentment and anger, are aided in their quest by mass-communication. In Rwanda in 1993, and Hitler's Germany much earlier, it was radio that spread messages of populist hate. Today's grassroots insurrectionists use Twitter and Facebook to hammer their message home.

In some ways, Twitter has been a force for good, helping to overthrow tyrants and expose corruption, spreading ideas and expanding people's social and professional networks. But the flipside is that it provides those peddling conspiracies - the people Robert Harris describes as society's "psychopaths" - with a voice they otherwise never had, and a community they might otherwise never have discovered. Those on the extremes of the debate can become the mainstream, fostering hatred, trolling their enemies and spreading terror, so resulting in an upsurge in attacks on minorities, whether the brick-throwing at Angela Eagle's window or the surging antisemitism. The Jewish community has always relied on the protection of the British state. In this coming post-factual age, the safety and security of our community has never been more uncertain.

Mr Gradgrind was, of course, a repulsive character, motivated by self-interest and entirely heartless. But history tells us that a fact-free world –- devoid of certainties and at the whim of the mob - is every bit as terrifying as Dickens's bleak picture of repressed Victorian England.

David Byers is assistant news editor at The Times