You may think Hungary is a faraway country. Small and landlocked, it has a baffling Finno-Ugric language few outsiders master. What do its corruptions and conspiracy theories have to do with us? When I was last in Budapest in August, I met Marta Pardavi. I worried about her and her friends in the Hungarian human rights movement, but I did not think I needed to transfer my fears back to Britain.

To understand her predicament, you must know that the ruling party, Fidesz, and its capo, Viktor Orbán, rigs the constitution, the electoral system, most of the media, the judiciary and Hungary’s cultural institutions. The handmaiden of autocracy is corruption. If Hungarians want to see a doctor or win a government contract, they have learned to reach into their pockets. Budapest is not a European capital now: it is Moscow on the Danube.

Because any sane electorate would throw him out, Orbán needs an enemy to scare Hungarians into voting for him on 8 April. He has come up with a novel combination of anti-Jewish and anti-Muslim bigotry. A classic dish with a modern twist, you might say: two “others” for the price of one.

The state has saturated the country with propaganda portraying the liberal Hungarian-Jewish financier George Soros as a menace to the nation. The rootless cosmopolitan is planning “to resettle at least one million immigrants annually” in the EU in general and Hungary in particular, Fidesz warns. As Soros does not command a government, Fidesz would have struggled to explain how he could flood Europe with Muslims. It’s as if UK ministers were pretending the choice before the electorate was between the Conservative party and Human Rights Watch.

But Orbán rarely has to explain. Most TV stations and newspapers obey the government and their hack propagandists have worked to turn the marginal NGOs Soros funds, with no power beyond the ability to seek judicial review of the treatment of refugees, into agents of a supernaturally powerful Jew. When I met Pardavi, the state-sponsored attacks on her Hungarian Helsinki Committee were so extreme they appeared to me to be an incitement to violence. She shrugged and said that was the price of working in Hungary. The climate has turned colder since the summer. If Fidesz wins on Sunday, it has promised laws that will treat NGOs as threats to national security.

Meanwhile, someone is running black ops against the Helsinki Committee and the Civil Liberties Union for Europe. Imposters posing as sympathisers have tried to trap human rights workers into making off-the-cuff remarks Orbán can twist and use against them.

Jewish groups protest against Jeremy Corbyn at the Houses of Parliament after he was accused of antisemitism. Photograph: Anadolu Agency/Getty Images

You may Hungary is a faraway country, but Steve Bannon does not think so. He praised Orbán as “the most significant guy on the scene right now”. Orbán showed how Angela Merkel’s decision to allow columns of refugees to march across Europe could create huge opportunities for the far right. And not only in Hungary and Poland, whose government is imitating Orbán’s tactics with dog-like devotion.

Although no one could be further from a demagogue than Theresa May, it remains a matter of record that the Brexit campaign won with the help of the fake claim that Turkey was about to join the EU – two years on and it’s still outside – and with posters depicting the coming Muslim invasion. Beyond these scares lie faint signs of trouble to come. I have watched men and women I once admired turn from principled opposition to Islamist reactionaries into opponents of any version of Islam. I am talking about a handful of people, but consider how their numbers may grow on the “respectable” right.

The EU has been its “other” since Margaret Thatcher’s last days. Where will the right turn when we leave? The terms of the divorce will be so bad that perhaps the right will carry on blaming the EU for its failures for years to come. But if it needs a new enemy to motivate its base, one only has to look to Orbán or Trump to guess who that “other” may be.

As for Orbán’s cosmically evil Jews, turn to the British left. For a generation, its dominant voices have failed to draw a line between criticism of the Israeli occupation of the West Bank and fascist ideology. Like rightwingers who no longer care about the difference between opposition to radical Islam and anti-Muslim bigotry, they accept no restraint.

It cannot be repeated often enough that antisemitism is a racist theory of power. Leftists have always been susceptible to the “socialism of fools”, because in their worst moments they believe democracy and human rights are shams hiding the capitalist puppet masters. It is all too easy to move from saying the puppet masters are the “capitalists” to the puppet masters are the Jews.

To stay only with Jeremy Corbyn, he has taken the shilling of the Iranian state, which is not only antisemitic but misogynist and homophobic, defended a more than usually vicious vicar, who said Jews were the secret conspirators behind 9/11, a mural that paid homage to Nazi conspiratorial “art” and a Palestinian activist who revived the medieval conspiracy that Jews drank the blood of Christian children.

Rather late in the day, he decided it was politically prudent to repent. But mark the reaction of his supporters last week. They did not believe Corbyn’s contrition was sincere. Thousands signed a letter stating he was a victim of a “very powerful special interest group”. Or as Christine Shawcroft, a member of Labour’s national executive committee, put it after defending an alleged Holocaust denier (as you do): “This whole row is being stirred up to attack Jeremy.”

In Budapest, the far right has Jews plotting to destroy Christian Europe by bringing in Muslims. In London, the far left has Jews plotting to destroy the Labour leader with fake accusations of racism.

Hungary is a faraway country, you say. Not so faraway.

• Nick Cohen is an Observer columnist