One of the genies uncorked by the referendum on the EU has been low-lying fascism and extreme nationalism. This is not to say that all leavers were racists. Far from it. But one of the political forces that have been unleashed is a form of dangerous nativism that unchecked will threaten us all.

It’s clear from the barrage of reports that a form of bigotry in everyday conversation is being legitimised. It is not racist to worry about high levels of immigration but a climate of fear is being created in the name of leavers. There are reports of schoolchildren terrified of being deported. “Polish vermin”, “Paki cunt” and “send them home” seem to be becoming something that immigrants and non-whites have to once again have to endure.

Monday night’s BBC news report featured a neo-Nazi in a balanced piece about the fallout for eastern European immigrants of Brexit in Leeds. Outside a Polish shop, in an interview a heavily inked Lee described himself as a “nationalist” and a “fascist”. He openly displayed his swastika tattoo and talked of a “sense of relief” after the Brexit vote. It was, said Lee, time to “take our country back”.

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For the leave campaigners, it must weigh on their conscience that their slogans have been easily adopted by the far right. That’s the trouble with words, you never know whose mouth they have been in. Seven years ago the country had an impassioned debate over the right of the British National party’s Nick Griffin to appear on Question Time. Griffin did appear. His cause died a political death, eviscerated by his fellow panellists’ fury.

The aftermath of the Brexit vote threatens to reanimate that corpse. It is increasingly clear that the language of extremists is becoming part of the British street. Words are weapons-grade material. They can be made into political bombs. How long before “send them back” becomes a line in a manifesto that suggests voluntary repatriation for the last wave of European migrants?

The cause of free speech is worth defending. But it’s not absolute. Britain’s politicians have long policed the boundaries of political debate. Those who resort to fists and baseball bats have been excluded. However this referendum has seen not-so-coded appeals to racial and ethnic resentment surface. Nigel Farage’s poster, which resembled a scene from a Nazi propaganda video, with the strapline “Breaking point” was such a loathsome entreaty.

Those who trade in xenophobia are on the march in Europe. Extremists, playing on people’s cultural and economic insecurity, have been gaining ground. In Sweden the extremist anti-migrant Swedish Democrats are making the political weather. In Austria, the extreme right came within a whisker of winning the nation’s presidency. Marine Le Pen, the leader of the French far-right Front National party, described the British Brexit vote as a “victory for freedom”. She put the union jack on her Twitter homepage.

Like Donald Trump it is presented as “no filter” politics, a refreshing blast of common sense. If only we could say the unsayable then we’d be free. That’s the problem. These so-called nationalists love their country so much that they would push it over a cliff edge, risking everything so that the people can be themselves alone. Do we want such nativist furies to be guiding our politics in years to come – a time when we face some of the most complex and difficult issues of our time? I think not.

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It is a paradox that the victory of the secular age is that political arguments are won by beliefs rather than facts. No longer is debate rooted in opinions that can be tested by rivals presenting a case based on empirical evidence. Referendums, which can unlease pent-up passions and where small conspiracies can seize the democratic process, are particularly well suited to this subversion. Yes the people have spoken. But the facts did not.

Proper democracy is far more than a ballot. A referendum can be a “safety valve” but it should not be the locomotive that drives the politics. That democratic process must include deliberation, mature institutions and checks and balances. There are big questions to answer: on why our economic model of growth has failed to deliver for many people. On what our role in the world should be. On how we need to come together – rather come apart – as a country. This requires an atmosphere of civil rational debate.

The far right preys on the weakest members of society and by letting anti-immigrant rhetoric bed in we are eroding civil rights not strengthening them. We must take into account how seductive extreme messages of hate can be. Any comparison with religious fundamentalists fails to recognise that they could never take over mainstream political debate. Extremists can do this simply by popularising racism. This is the arsenic in the water supply of any nation. Britain should be wary of being seduced by the charms of people who trade in the politics of poison.