"You only think I guessed wrong! That's what's so funny! I switched
glasses when your back was turned! Ha ha! You fool! You fell victim to
one of the classic blunders! The most famous is never get involved in a
land war in Asia, but only slightly less well-known is this: never go
in against a Sicilian when death is on the line! Ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha! Ha ha ha..."

Vizzini, from The Princess Bride

Aside from not getting involved in a land war in Asia (I think the US has found that out a few times in the last few decades), another classic blunder is starting a trade war when your country is in a recession (or, day I utter the word, depression). The knee jerk reaction to cut of imports of goods to save your domestic manufacturers or barring from workers to protect your domestic labor market may feel good. But they have the complete opposite effect of what is intended. They invite retaliation which kills leads to trade wars and has the effect of deepening an prolonging global downturns. Surely, we learned that in the 1930s with the disastrous Smoot-Hawley tariff policy in this country. World trade declined 66% in five years during the trade war of the 1930s and Smoot-Hawley certainly was one of the reasons why.

The UK's Prime Minister seems to have flunked world history. Why else would they be announcing plans to halve the number of high-skilled work visas in that country? Perhaps some people don't consider work visas a form of trade, but I would counter that labor is THE most important component of production at many companies. Payroll is often a company's most expensive overhead item and finding suitably skilled workers is frequently a company's biggest challenge in remaining competitive. Visa policy IS trade policy.