This article must begin with a mea culpa. When British voters decided in June that they wanted to depart the European Union, I agreed with the conventional wisdom that the British economy would probably slow and that uncertainty put it at risk of recession.

Advocates of “Brexit” argued that was hogwash, and the early evidence suggests they were right. For example, surveys of purchasing managers showed that both the British manufacturing and service sectors plummeted after the vote in July, yet were comfortably expanding in August and September.

But the events of the last couple of weeks suggest that British leaders are drawing the wrong conclusions from the fact that their predictions proved right. The British currency is plummeting again, most immediately because of comments from French and German leaders suggesting they will take a tough line in negotiating Brexit. But the underlying reason is that the British government is ignoring the lessons from the relatively benign immediate aftermath of the vote.

The British pound fell to about $1.24 on Friday from $1.30 a week earlier and continued edging down Monday. Even if you treat a “flash crash” in the pound on Asian markets Thursday night as an aberration — it fell 6 percent, then recovered in a short span — these types of aberrations seem to happen only when a market is already under severe stress. (See, for example, the May 2010 flash crash of American stocks, during a flare-up of the eurozone crisis).