The floor of Boris Johnson’s car - recently captured by an enterprising photographer - contains little of note: water bottles, empty coffee cups and receipts are strewn across the Toyota Previa. But among such banal paraphernalia lies a copy of Britannia Unchained, a free-market tract co-authored in 2012 by five recently-elected Conservative MPs: Kwasi Kwarteng, Priti Patel, Dominic Raab, Chris Skidmore and Liz Truss.

The 152-page book excoriated the UK’s “bloated state, high taxes and excessive regulation” and, most memorably, derided British workers as “among the worst idlers in the world” (“We work among the lowest hours, we retire early and our productivity is poor. Whereas Indian children aspire to be doctors or businessmen, the British are more interested in football and pop music.”) The UK, it declared, should “stop indulging in irrelevant debates about sharing the pie between manufacturing and services, the north and the south, women and men”.

Though Britannia Unchained did not advocate EU withdrawal, it exemplified the spirit that would later animate Brexit. Rather than learning from Germany and the Nordic states, as social democrats advocated, it urged the UK to emulate Australia, Canada and the Asian “tiger economies” (Hong Kong, Singapore, South Korea).

Whether or not Johnson has read the treatise, its influence on his new cabinet is marked. Two of the co-authors, Patel and Raab, now hold two of the great offices of state (the Home Office and the Foreign Office). Truss, perhaps the most passionate libertarian of the quintet, has been promoted from Chief Secretary of the Treasury to International Trade Secretary, while Kwarteng has been named business minister and will attend cabinet (leaving only Skidmore absent from the top table).

The new Chancellor, Sajid Javid, is not one of Britannia Unchained’s authors but he has often echoed its turbo-Thatcherite spirit. Indeed, his original ideological heroine was the late US philosopher Ayn Rand, an unashamed advocate of “greed is good” economics. In the courtroom scene of Rand’s book The Fountainhead, which Javid often recalled, the main character Howard Roark declares: “The man who attempts to live for others is a dependent. He is a parasite in motive and makes parasites of those he serves. The relationship produces nothing but mutual corruption.”

Now, however, Javid emphasises that he is “not a Randian” and “never has been” and that “altruism is one of the reasons I’m in government”. In common with other Conservatives, he has largely abandoned austerity economics and has advocated borrowing £50bn to invest in housebuilding. But Javid has continued to endorse such Britannia Unchained-style policies as reducing corporation tax from 19 per cent (the lowest rate in the G20) to 12.5 per cent and abolishing the 45 per cent rate of income tax.

Johnson himself is an ideological magpie, embracing or dispensing with policies based on his own self-advancement. But he has long had a libertarian streak, one witnessed during his 2013 Margaret Thatcher Lecture when he declared that “some measure of inequality is essential for the spirit of envy” that is, “like greed, a valuable spur to economic activity”.

More recently, at the first Conservative leadership hustings, Johnson made a Rand-esque boast: “Can you think of anybody who stuck up for the bankers as much as I did? I defended them day in, day out, from those who frankly wanted to hang them from the nearest lamppost.”

The Britannia Unchained cabinet contrasts with the approach pursued by Theresa May, who often denounced libertarianism and sought to rehabilitate the state as an economic actor. The former prime minister often framed Brexit as an opportunity to end the free movement of people from the EU. Johnson’s government will likely pursue a more liberal approach to immigration: ending the “tens of thousands” net migration target and potentially introducing an amnesty for some illegal migrants (of note is that Javid, Patel and Raab are all the children of immigrants, while Johnson was born in New York).

But crucially, for the free-market right, Brexit has a higher ideological purpose. The authors of Britannia Unchained viewed the Cameron years as largely a wasted opportunity. Though public spending was sharply reduced, taxes and regulation were not. The Leave vote of 2016 provided a new vehicle for Thatcherism 2.0: Brexit.

In May 2016, Patel, the then employment minister, remarked: “If we could just halve the burdens of the EU social and employment legislation we could deliver a £4.3bn boost to our economy and 60,000 new jobs.”

For libertarians, the appeal of a no-deal Brexit, as threatened by Johnson, is precisely that it could create the conditions to impose policies unachievable in normal times (just as the 2008 financial crisis helped enable austerity). As Milton Friedman once remarked: “Only a crisis - actual or perceived - produces real change. When that crisis occurs, the actions that are taken depend on the ideas that are lying around.”

The dream of unchaining Britannia may yet collide with the reality of a withered parliamentary majority and a polarised electorate. But a book once dismissed as an eccentric manifesto increasingly resembles an eerie preview of Britain’s future.