Boris Johnson has made his career out of creating myths about Europe. With Theresa May’s job again within his ever-ambitious grasp, he’s not going to stop doing it now.

The foreign secretary’s speech this week will conjure the prospect of a “liberal” post-Brexit free trading order. In this Johnsonian vision, Britain will be freed from politically driven European regulatory systems whose true purpose is only to create a unified Europe. Instead, he says, Britain will be able to create its own regulatory regimes to align issues such as social rights, the environment and energy with the country’s post-Brexit global free trade aspirations.

The problem is, it is about as realistic and fact-based as the claims Johnson made three decades ago when he was a tyro Eurosceptic journalist in Brussels. Those were the days when Johnson’s ever colourful and mocking stories about EU plans to standardise condom sizes, ban British potato chips and blow up its own headquarters helped fuel a Eurosceptic mood in which everything about the union was axiomatically “bad for Britain”.

Thirty years on, Johnson is still at it. He now claims leaving the EU will bring economic gains providing Britain is able to make its own regulations unencumbered by too close a relationship to the EU single market and customs union. This too is the triumph of hope, not to say self-delusion, over reality.

It is true that a few – mostly not very successful – European political leaders still dream of a United States of Europe and see “more Europe” as the reflexive answer to every problem affecting the union and its people. But the vast majority of leaders these days are pragmatists about the rewards of working together, not idealists.

Crucially, the EU single market and customs union means that many of the main blockages to the free flow of trade across Europe have been removed. Modern Britain has done well out of those flows. In that sense, a “liberal” Britain should be staying in or as close as possible to the EU. The real risk is that, by turning its back on EU regulatory systems, post-Brexit Britain deregulates things such as workplace and environmental safeguards in a desperate search for a trading advantage that would soon hit British workers and citizens badly.

Intoxicated by the myth of his own superior intelligence, or simply by the allure of another tilt at the Conservative leadership, Johnson seems incapable of understanding these realities and dangers. Of course there could be a “liberal” form of Brexit – cleaving close to the EU in a Norway-style deal that would give Britain the material benefits without a say in the working of the system. But this is the opposite of the version Boris Johnson is offering.