With no deal, trade relations between Britain and the European Union would revert to the very basic rules of the World Trade Organization. These entail that neither side is allowed to treat the other more favorably than it treats other trade partners around the globe. If Britain steps out of the union without any bilateral trade deals, a customs regime would have to be installed between Britain and its European neighbors. In the interim, thousands of businesses on both sides, and millions of customers, will be thrown into a costly confusion. At least my insurer has a plan; many other companies are still struggling to find one.

The old, once-amusing British headline “Fog in the Channel — Continent Cut Off” could finally come to bear some truth, particularly for Germany‘s key industry: automakers. Within Europe, Britain is by far their biggest market. Last year auto manufacturers based in Germany exported three times more cars to Britain than they did to China, according to their trade association’s data. The auditing firm Deloitte believes that the number of German cars sold to Britain could drop from 800,000 to 550,000 annually, endangering 18,000 German jobs.

The auto industry is a great example of just how complicated and messy a “hard” Brexit will be. It’s not just that fewer British customers will buy German cars. It’s also that well-established, just-in-time supply chains could be destroyed. As The Guardian reported, the crankshaft of a BMW Mini crosses the Channel three times before it becomes part of the finished car: The cast is made in France, then goes to a BMW plant in Warwickshire, where it is drilled, then travels to Munich, where it is set into the engine. The engine finally is shipped back to the Mini plant in Oxford, to be mounted into the car. With a customs regime in place, all those cross-Channel trips will become much more expensive.

Brexiteers claimed that Britain could shake off the union’s principle of free movement of people yet somehow maintain the usual level of free trade with the continent. Those were pipe dreams. So were expectations that as the hour of Brexit approached, the European Union would bow to Britain’s demands.

Despite the damage Brexit will cause in the remaining 27 countries of the union, they are unflinching in their message to London: This will be painful for both of us, but we can’t let you change the rules. Germany, which sells far more cars to the rest of the union than to Britain, has insisted on this hard line throughout the talks. Germany doesn’t want to lose British buyers, but it can’t afford to undermine the common-market structure that undergirds its sales to the rest of Europe.