Most countries want to keep out products that are potentially unsafe (such as. electrical goods, medicines, recycling waste or GM crops) or unethically sourced (such as products made by slave labour).

That seems a perfectly legitimate policy — though if we find that a country imposes stricter product standards on importers than it imposes on its own producers, that is a sure sign of safety masquerading as protectionism.

So how do we know what safety and ethics objections are legitimate and not merely an excuse for protectionism? Are the concerns about America’s use of hormones in cattle, chlorination of chicken, or exports of genetically modified cereals legitimate health fears or just an excuse to block US agricultural products? And is America justified in refusing meat products from countries with much lower animal welfare standards, or manufactures from those with poor human rights records?

There are no easy answers. Safety concerns can be exaggerated, and standards twisted in order to keep out specific competitors. That is why product standards are one of the biggest sources of WTO trade disputes.

Given the opportunities for abuse, our general aim should be to stop individual countries imposing their own standards on other people’s products. International agreements might be a better way to achieve the stated aim.