If you want to understand something about the demise of the international rules-based order, it’s worth thinking about olives. They may not be making headlines in the UK but an increasingly toxic relationship between the EU — the world’s dominant producer — and the US — an olive minnow — tells us every-thing we need to know about our future trade prospects.

The olive tree may have originated in the Levant but it is very much a European plant, both in terms of its botanical name — Olea europaea — and Europe’s current share of the olive oil and table olive markets. According to the International Olive Council, the countries of the European Union together pressed, extracted and refined 2.2 million tonnes of oil this past year, accounting for more than 70 per cent of global production. They also harvested approaching 900,000 tonnes of table olives, not far shy of a third of the global total.

Harvesting is done both by machines, which shake the trees vigorously and catch the falling fruit in large nets, and by hand. In Greece, where there are plenty of olives but olive grove ownership is hugely fragmented, there’s a bias towards the latter. It’s a decision lubricated (if that’s the right word) by the plentiful availability of cheap seasonal migrant labour, largely from Bulgaria and Romania.

Indeed, the whole process of Greek olive oil production is a microcosm of globalisation: once the fruit is harvested and the process of extracting and refining is complete, a lot of Greek olive oil is then shipped in bulk across to Italy, where it is typically blended with olive oil from Italy and elsewhere before being placed in fancily-branded bottles and tins to be sold on the shelves of, say, Waitrose.

The iPhone may be designed in California and assembled in China but, as far as globalisation is concerned, the olive got there first: grown in Greece, harvested by Bulgarians, blended and packaged by Italians and purchased by Londoners. And our greater awareness of the health benefits of the so-called Mediterranean diet — partly a side-effect of more frequent holidays in that part of the world — has led us to ditch the lard of yore in favour of the olive nectar. No longer is olive oil solely available in the local chemist for the singularly revolting purpose of softening earwax.

Which brings me to the American share of the olive market. Its oil production is minuscule, a mere 0.5 per cent of the global total. Its share of world trade in olive oil is less than one per cent. On table olives it does marginally better, with a production share of just over two per cent, but that’s still tiny. In effect, the US is to olives what the UK is to laptop computers: largely irrelevant.

Yet this hasn’t stopped US olive producers from claiming that their Spanish rivals have been dumping their olives into the American market and, as result, harming the interests of local olive growers. The US Commerce Department responded last year by imposing countervailing tariffs of around 35 per cent on imports of Spanish olives. To date, however, there’s been little evidence of any real change in the flow of olives from Spain to the US.

Last week, a representative from the Olive Growers Council of California argued in favour of 100 per cent targets as part of a “bundled” tariff response to Washington’s long-running dispute with Brussels over Airbus (who knew a link could be made between an ancient fruit and a modern aircraft?)

I’m not for one moment suggesting the Europeans should be given a clean bill of health when it comes to dumping olives elsewhere. There is, however, something odd about policymakers in a country whose consumers clearly like to consume Spanish olives (even after a significant price increase, thanks to last year’s tariffs) choosing to ignore consumer interests while supporting fledgling producers who don’t have the capacity to satisfy the local market, let alone markets elsewhere in the world.

It may be difficult for the UK to seal a trade deal that supports British consumers as much as it protects the US

Maybe Californian producers hope to do for olives what their winemakers did for pinot noir. The US has a long history of using “infant industry” arguments to support homegrown businesses at the expense of foreign competitors. But olives? Really? The laws of comparative advantage surely suggest the US should let southern Europe stick to its olive groves while California should focus on Google, Apple and Tesla. By doing so, Californians would, on average, become still richer, allowing them to buy even more Spanish olives for their delectation and delight. That’s how trade specialisation is supposed to work.

In current circumstances, these core principles of international trade are in danger of being ignored. And that is ultimately bad news for all of us. Mercantilism — the idea that exports should ideally always be higher than imports and that trade flows should be “distorted” in the home nation’s favour through the copious application of tariffs and quotas — was all the rage in the 200 years before the onset of the Industrial Revolution. It gradually died away during the 19th century only to reappear, at huge economic cost, during the interwar years.

The post-war economic boom happened precisely because institutions like the General Agreement on Tariffs and Trade managed to deliver massive tariff reductions, leading to an enormous expansion of bilateral trade flows and, eventually, to the global supply chains that have become a key characteristic of modern-day globalisation. Consumers have benefited almost everywhere.

Mercantilism, however, is back. It’s a natural result of an “America First” policy in which Washington is no longer quite so interested in sticking to the old international rules of the game. As such, as the UK prepares to leave the EU, it may prove difficult for Whitehall’s trade novices to lock horns with their Washington equivalents and emerge with a transatlantic trade deal that backs British consumers and producers as much as it protects the interests of their US equivalents. If so, Boris Johnson may wonder whether he might have been better off reincarnated as an olive.