The English air is as foul as it has been at any point since my childhood. It is as if the sewers have burst. The Leave campaign has captured the worst of England and channelled it into a know-nothing movement of loud mouths and closed minds. It is easy to mock, but essential to fight, because the new right could win a victory that may never be reversed.

If you do not want to be saying: “I want my country back” for the rest of your life, my best advice is not sell it out on Thursday.

You get a measure of the unashamed charlatanry of the men who ask for your votes, if you remember that the leaders of the Leave faction once posed as compassionate conservatives. Not so long ago, Boris Johnson wanted an amnesty for illegal immigrants so that frightened people living beyond the rule of law were not “lost in the undergrowth”. That was when he was mayor of liberal London. Now Johnson is using fear of immigrants as a crowbar to force his way into Downing Street and Nigel Farage can ruffle his pupil’s hair with paternal pride and tell Channel 4 News he “couldn’t be happier” his boy is following “my strategy”.

I can think of no other time in our history when a secretary of state could get away with dismissing every informed objection with: “I think people in this country have had enough of experts.” Our new right excuses Michael Gove because it knows its best hope of victory lies in the embrace of the irrational.

I could go on. Vote Leave began by insisting it wanted nothing to do with a Ukip that echoes the propaganda of fascist Europe. (Inadvertently, of course. For as the Tory press keeps telling us the notion that the British right is standing by while neo-Nazism grows here is an appalling libel.) Matthew Elliott, Vote Leave’s director, promised a “positive” and “internationalist” vision for Britain. We do “not need to focus on immigration”, added Dominic Cummings, his campaign director. The essential task was “to neutralise the fear that leaving may be bad for jobs and living standards”.

With a cynicism, which again I can find no historical parallel for, it has now decided to fan fear instead. Vote Leave realised it could not have won a rational argument about jobs and living standards. As thousands of economists have warned, it makes no sense to say that the country will be better off if it turns its back on the richest single market in the world.

We will take a hit. And the poor will be hit hardest.

The once “positive” and “optimistic” campaign has therefore poisoned rational debate by endorsing paranoid populism, the spirit of our age.

I am not seeking to make a partisan anti-conservative point. Paranoid populism is a general sickness, as common on the left as the right. You hear it when audiences on Question Time scream that all politicians are liars and crooks, then sit back expecting to be applauded as heartily as they applaud themselves. You see it in the below-the-line comments desperate editors publish. You find it everywhere on social media, in the authoritarian demands of Scottish nationalists and English leftists that the BBC sack journalists who report uncomfortable facts and in Donald Trump’s smears of all who cross him.

Paranoid populism’s defining principle can be summarised in a paragraph. No one contradicts me in good faith. My opponents must be lying. They must be corrupt. They are more than merely mistaken, they are degenerate.

You only have to see the neurotically relentless coverage of immigration in the Daily Mail and Express or the antisemitism on the left to see the final mobiliser of paranoid opinion: racism, the oldest and most effective recruiting sergeant there is. If you wish, we can have learned discussions about how the web allows us to live in enclaves, which black out alternative points of view. And indeed it is worth talking about how those who scream the loudest about politicians being trapped in Beltways and Westminster bubbles, and damn “experts” for hiding in their ivory towers, have willingly locked themselves in maximum-security prisons of the mind, from which there is no escape.

You can accept, too, that there are good reasons to scream with rage. Britain has had the largest immigration in its history, after all, and not only racists worry about the consequences. But however fair minded you wish to be, you cannot deny that the Leave campaign has had to head into the sewers of conspiracy theory and race politics because it had nowhere else to go.

It now resembles nothing so much as a trolls’ alliance. Vote Leave damns all its critics as liars, and corrupt liars at that. They have been bought and sold with Brussels gold and are nothing more than “paid-up propaganda arms of the European commission”.

As so often in the past, those who claim to be fighting the elite on behalf of the masses are the most manipulative of all. Baffled broadcasters, who do not understand the new world, have politely wondered why Johnson and Gove are claiming pensioners will be left to suffer as the NHS is overrun by 77 million Turks, when there is absolutely no prospect of Turkey joining the EU. The answer is simple: they do it because they know that playing on racial fear works. They do it because they are confident that any “expert” the BBC can put on air to contradict them can be dismissed with Govean scorn as a liar and a fraud.

The true scorn of the right is for the people it presumes to represent. In the name of defending Britain, Brexit will destroy Britain, if Scotland then leaves. In the name of defending Britain, Johnson, Farage and Gove will break the unity of the west and put a wolfish grin on the face of Vladimir Putin. In the name of defending Britain, Brexit will start a rolling economic, constitutional and diplomatic crisis, which its authors do not have the smallest idea how to solve.

The air is foul now. But imagine how much fouler it will become as the nationalist right invents ever more fanatical conspiracy theories to explain away the troubles it has brought upon us. If you love your country, or even just think it is not such a bad place, do not hand it to sly men who betray the best of the English, while seeking to incite the worst in us.