On the face of it, it is just a foolish demand from an unknown councillor. Christian Holliday, a Conservative representing Burpham on Guildford Borough Council, set up an online petition this weekend demanding anyone still supporting EU membership after Brexit is charged with treason.

"Amend the Treason Felony Act to make supporting UK membership of the EU a crime," it reads. The Act would apparently be amended to include the phrases: "To imagine, devise, promote, work, or encourage others, to support UK becoming a member of the European Union" and "to conspire with foreign powers to make the UK, or part of the UK, become a member of the EU".

It's easy to laugh. Sometimes laughter is the only thing that keeps you in a tolerable mood when your country seems to be having a protracted emotional breakdown. And yes, we have always had overexcited, foolish councillors around us. But Holliday's totalitarian petition should not be viewed in isolation. It stems from a history of eurosceptic thinking which has always viewed the lending or giving up of sovereignty as intrinsically unpatriotic. For some reason they do not feel the same way about bilateral treaties, or WTO membership, which also often involve giving up some sovereignty. But regardless of their consistency, this is a standard form of thought on the eurosceptic right.

It has been injected with steroids by the Brexit victory. What was once a fringe view now goes right up to the heart of government and the press. Brexiters' instinctive response to criticism is to first of all question people's patriotism and then accuse them of treason.

On Saturday night, Stewart Jackson, MP for Peterborough and parliamentary private secretary to David Davis at the Department for Exiting the European Union (DEEU), tweeted his outrage at "Remoaner whining" at that bastion of left wing activism, the Economist. He then added: "Cancelled my subscription. UK patriots shd do similar."

Again we see that same idea: To be patriotic is to demand Brexit on the hardest possible terms. To believe otherwise is to, at best, not love your country. And at worst wish to betray it. Once you accept the first interpretation, the second is never very far away.

This message is being amplified by the eurosceptic press. Take the front pages of the Mail and the Express last week when MPs dared to ask for a parliamentary debate on the terms of Brexit. "Damn the unpatriotic Remoaners," the Mail shouts, and their "plot" to "subvert the will of the British people". Note how it emulates the language of war: failure of patriotism, scheming fifth columns, the enemy within, the lionisation of the public and the assumption that all of them are on your side. Look at how the 52-48 vote has been redefined: the British public on one side and unpatriotic Remoaners on the other. The Express takes that idea to its logical conclusion. After all, if someone is acting to subvert the country, they have to be stopped. So it is natural that we "silence EU exit whingers".

Three things have brought us to this place: cynical political strategy, rampant nationalism and post-truth politics.

Look at the briefings against chancellor Philip Hammond by unnamed Cabinet colleagues in the Telegraph this morning. "He is arguing from a very Treasury point of view," the source said. "He is arguing like an accountant seeing the risk of everything rather than the opportunity."

It is astonishing to see ministerial scrutiny, especially from a chancellor, being framed in a negative context. The clear underlying thought behind the comment is that a commitment to Brexit should be the motivating force in Hammond's mind, with concerns about the likely consequences an afterthought.

We see the same thing across government. Trade body officials visiting Davis at the Brexit department report being taken aside by civil servants and told to go in saying that Brexit opens up many possibilities. If they enter making critical comments they are shown the door after five minutes. Any view outside of hard Brexit is intolerable.

Davis refuses to even acknowledge that membership of the single market even means anything anymore. Any talk of whether we will stay a member is met by the insistence that there are a "spectrum of outcomes". Boris Johnson says 'single market', as a term, is "increasingly useless". And May herself says "there is no such thing as a choice between 'soft Brexit' and 'hard Brexit'" when there quite demonstrably is. It is defined by membership of the which she, Johnson and Davis refuse to say out loud.

Emotionally, this is a defence mechanism. When Davis was responding to Labour's opposition day motion on Brexit last week the pound fell again as he spoke and then rose once he sat down. He quite literally acts against the national interest by speaking. When the evidence of the danger of your opinions is so obvious, perhaps the only option is to retreat into fiction.

They are dealing in the politics of the post-fact world. All that matters is the great historic mission of returning full sovereignty to Britain, even though such a thing is neither possible nor desirable.

These three elements – cynical political manipulation, nationalism and post-truth politics – are doing something dangerous to this country. On the national scale, they are driving us towards an economically catastrophic exit from the single market. But internally, on the social bonds between us, they are a poison, a poison which encourages people to mistrust and despise their neighbours on the basis of their politics. Those willing to engage in the talk of treason and lack of patriotism should urgently explore their conscience.

Ian Dunt is the editor of Politics.co.uk 

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.