One dubious perk of a job writing about politics is free books that no one else would choose to read. Often, ambitious MPs feel they ought to put their vision in print, regardless of whether or not they have one. These unsolicited manifestos are then dispatched to newspaper offices where they are mostly forgotten. Mostly, not entirely.

I recently found myself browsing one such volume, Britannia Unchained, co-authored by five Conservative MPs in 2012 who immodestly described themselves as “rising stars” on the sleeve. One, Dominic Raab, has risen to be secretary of state for Brexit, which is reason enough to revisit his back catalogue.

It is humiliating to land in a safety net, a sign of failure, but preferable to severe injury or death.

The premise of Britannia Unchained is that Britain, made torpid by a coddling state, faces decline unless it exchanges timorous risk-aversion for a spirit of buccaneering enterprise. This was not a new theme for Conservatism in 2012, but it has become a kind of mantra in the context of Brexit. Buccaneers, apparently, can’t sail while still anchored to Brussels. Freedom means nothing if it isn’t the freedom to sign trade deals, and EU membership (specifically, adherence to the common external tariff as part of a customs union) therefore amounts to intolerable bondage.

You might imagine that this view was anticipated by Raab and friends four years before the referendum. But no. Nowhere, not once, do the authors so much as hint that EU membership is a problem or that ending it forms part of the solution. There is stuff about venture capital, maths training and welfare reform. On the cruelty of a customs union – not a word. So what? People change their minds. They adapt to circumstance. Who cares that very recently the self-styled intellectual vanguard of Toryism thought EU membership was wholly compatible with national renewal? Now they see things in their proper perspective. The greatest obstacle to prosperity was not a skills shortage or fiscal mismanagement. No, it was the common external tariff all along.

And so we get to autumn 2018. The prime minister was due to set off today on a trip to sub-Saharan Africa with a trade delegation and a familiar pitch: “As we prepare to leave the European Union, now is the time for the UK to deepen and strengthen its global partnerships,” Theresa May said. This has become part of her shtick. She goes somewhere that isn’t Europe and declares that British commercial ambition soars beyond its continental neighbourhood.

Facebook Twitter Pinterest ‘Dominic Raab has risen to be secretary of state for Brexit, which is reason enough to revisit his back catalogue.’ Photograph: WPA Pool/Getty Images

Liam Fox can usually be relied upon to chime in with the assertion that 90% of global growth in the coming decade will be outside the EU. This is a popular Brexiteer statistic because it implies that the UK has made the far-sighted choice, switching out of the 10% European slow lane. That would be true if EU membership prohibited access to all other markets – if you could ship goods either within the EU or outside it, but never both. Plainly that is nonsense. Germany’s biggest trading partner is China. Berlin does not see its regulatory obligations to the single market as a brake on global exports.

Of all the nonsensical Brexit ideas to have acquired respectability through sheer force of repetition by Tory MPs, perhaps the flimsiest is this false dichotomy of “global” trade and EU membership. The common external tariff prevents EU members from signing bilateral agreements, but the compensation is being party to deals that Europeans negotiate as a bloc and, thanks to the sheer scale of the single market, on terms befitting an economic superpower. About 49% of Britain’s trade is currently with the EU. Another 12% is with 65 non-EU states that have free-trade agreements with Brussels. The most recent, with Japan, was signed in July this year.

There is no system for replicating those agreements after Brexit. Fox has racked up thousands of air miles crossing the Atlantic and the Pacific, eliciting bland statements of goodwill from overseas counterparts. But the number of deals he has successfully negotiated is a fat zero.

And that’s where reference to the World Trade Organization comes in: won’t that serve as a safety net? Perhaps, but only in the specific metaphorical sense of catching circus performers when they fall. It is humiliating to land in one, a sign of failure, but preferable to severe injury or death. If the ambition is to sustain cross-border trade at anything like its current level, or to provide an institutional framework in which the UK could replicate the clout it has as one of the EU’s biggest members, “WTO rules” are a fiction.

The WTO has become a rhetorical device, disconnected from the organisation behind the initials. It serves a purpose once fulfilled by the Commonwealth: the big thing involving many countries that, slathered in ignorance and seasoned with glibness, can be served up as an alternative to the EU. There was a Commonwealth summit in London in April from which the most memorable news was May apologising for the Home Office’s cruel treatment of British citizens of Caribbean origin who had been unjustly threatened with deportation. No trade agreements were signed.

When the Commonwealth is touted as an alternative to the single market there is, at least, a degree of honesty in the audible pining for empire. There is dismal pathos in Eurosceptic nostalgia for a time when “global” Britain was a territorial reality, not a branding exercise. There is no such excuse where the WTO is concerned. There are no misty-eyed historical or cultural associations, just a cynical diversion. No developed country trades purely on “WTO rules”. The idea that Britain should be the first to give it a go has gained currency in the Conservative party from sheer embarrassment. It is not a model for post-Brexit trade, it is a euphemism for failure to understand the true value of EU membership. It conveys a deep unwillingness to admit any kind of dependency on our European neighbours, even the mutually beneficial dependency of the single market – the largest, most sophisticated free-trade zone in the world, conceived and driven in large part as a British initiative, by Conservative governments.

This is the sad island where a generation of Tories find themselves intellectually discredited and marooned. They wanted to unchain Britannia and they ended up uncoupled from their own history, unmoored from basic geography, and adrift from economic reality.

• Rafael Behr is a Guardian columnist