What’s key to the very bad results is, instead, the disruption that might come with a hard Brexit. Right now, goods flow into and out of Britain with minimal frictions. After Brexit, there would have to be customs inspections, and the UK doesn’t have remotely enough customs infrastructure to do the job. The result would be huge delays at Dover and other ports, with queues of trucks backing up for many miles on motorways, just-in-time production massively disrupted, and more.

That disruption is what’s driving the terrible scenarios. Notice that this analysis says that the costs of leaving the EU are much higher than the GDP that would have been foregone if Britain had never entered the EU, and therefore had the customs infrastructure to deal with trade flows in place.

OK, that’s what I understand about the BoE analysis. What do I think about it?

2. Would it really be that bad?

So, about the BoE’s purpose in issuing this report: if it wasn’t intended to scare people, the Bank was extraordinarily naïve in not realizing how it would be reported and read. They really led with their chin here.

On the substance: I’m skeptical about the supposed effects of trade on productivity. I know that there’s some evidence for such effects; trade seems to favor more productive firms. But relying a lot on effects we can’t model seems dubious.

In particular, I have strong memories of the openness-growth debacle of the 1990s. At the time, there were many statistical studies purporting to find that open, outward oriented developing countries had much higher growth rates than inward-looking economies. This was interpreted to mean that countries that had tried to industrialize by protecting domestic markets could achieve Asian-type growth rates if they liberalized trade.

As it turned out, the supposed statistical evidence on openness and growth was quite suspect. And when massive trade liberalization happened in places like Mexico, the hoped-for growth miracles didn’t materialize.