Last week, an unelected special adviser delivered one of the most political and controversial speeches made by a British public official in recent times. It claimed, in justifying Brexit, that 19th-century political notions – the nation state with absolute sovereignty and wholesale independence of action – extended unchanged into the 21st century and were supported wholeheartedly in Britain. This betrayed a combination of ignorance, self-deception and vainglory that will ill serve our country.

David Frost, Britain’s lead Brexit trade negotiator, plainly had a rough time in an earlier incarnation in Brussels, drawing the conclusion that the EU is a clunky disaster – although generalising one’s own personal experience to inform your country’s negotiating stance is rarely a good guide to action. It must be congenial for the prime minister that his lead negotiator plainly thinks that his boss represents the acme of political genius. According to Frost, Boris Johnson’s approach to Brexit combines an ability to read the runes of the British with putting into place the enduring philosophy of the 18th-century, ultra conservative politician Edmund Burke.

In Frost’s romanticised view of Britain, Leave voters represented a populace unanimously anxious to recover the power of constitutional institutions sanctified by centuries of tradition and now threatened by the dark intentions of continental Europeans. We so love the royal prerogative, the Lords, the first post the past voting system and the monarchical powers of the prime minister that we would rip up our relationships with the EU. He continued: “We bring to the negotiations not some clever tactical positioning but the fundamentals of what it means to be an independent country. It is central to our vision that we must have the ability to set laws that suit us – to claim the right that every other non-EU country in the world has.”

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But this is bunk, even allowing for the posturing that inevitably frames the beginnings of any such major negotiation. To interpret the Leave vote as vast affection for the feudal trappings of an unwritten constitution to the degree that we want to stand in belligerent opposition to Europe, and make ourselves poorer in the process, is to descend into fantasy. It is a bewildering misreading of contemporary reality.

It may be true that loyalty to a Burkean vision of the British state existed among conservative Eurosceptic intellectuals. But it hardly describes the motives of the over-50s throughout Britain, in particular in the marginalised English coastal and former industrial communities characterised by declining life expectancy, low wages and low skills, who provided much of the Leave vote. Theirs was a justified cri de coeur about a stagnating present. A generalised nostalgia about the Britain that stood alone in 1940 and went on to create the soothing certainties of the 1950s, coupled with dislike of mass immigration, completed the Brexit mindset. But those under 50, especially in large conurbations dependent on openness and liberal exchange, thought the mindset baleful nonsense. They understand today’s world. Frost speaks at best for part of Britain, a fact a wise public official would acknowledge.

Play Video 1:38 'There is no need for a free trade agreement': Boris Johnson outlines UK stance after Brexit – video

Nor in 2020 has any state the independence and freedom to make its own laws, especially over trade. He may not have noticed but the exchange of goods and services has always been attended by concerns about standards and quality. The more countries try to gain from trade, the greater the concern to ensure common rules apply.

This necessarily inhibits the capacity to make independent law; a country may decide it only wants to meet certain environmental standards by 2050, but if it wants to sell its goods in countries that have set a target of 2030 it has to fall into line. A better option is for a group of countries to agree a common date in a trade agreement. An even better option is to establish a treaty framework in which such considerations – across as many goods and services as possible – are under constant appraisal to achieve common standards, so maximising trade. You could call such an arrangement the EU’s customs union and single market, if you like, but Burke would have disapproved, so obviously Britain can’t be a member.

But Burke’s world of independent national sovereignty in which Britain could send a gunboat to force China to import opium and sequester Hong Kong has disappeared. We now have two aircraft carriers, but they are dependent on US planes and in any case could not be deployed independently in war.

Every major current challenge – from taxing big tech to protocols for autonomous vehicles – requires international collaboration, joint action and common regulations. Creating them is painful and involves many compromises, as Britain will learn again at the Cop26 climate change talks it is hosting later this year. Canadians are keenly aware of the difference between their trade agreement with the EU and the one they have been bullied into by the US. They yearn for the kind of power the countries of the EU have developed.

The task in the decades ahead is to sustain and develop such structures and so allow citizens in every country to be better governed. It may stick in Frost’s 19th-century craw, but the EU, under tremendous strain intensified by Britain’s withdrawal, is precisely such a structure.

The British political debate is not helped by part of Britain’s left being obsessed by similarly 19th-century constructs – the notion that it is possible and desirable to use a wholly sovereign nation state to build a socialism whose statist structures require no compromise either internally or internationally. The British left may or may not succeed int devising a philosophy for the 21st century that marries values and policy with the actual interdependencies of our times but for the moment it is irrelevant.

What counts is the thinking in the court of King Boris. The musings of one of his most obsequious courtiers last week were not comforting. Prepare for a very hard Brexit and careless insouciance from those delivering it.

• Will Hutton is an Observer columnist