Frankly I don’t know why the British media made such a big fat fuss last week when I accidentally flattened a ten-year-old Japanese rugby player called Toki. He got to his feet. He smiled. Everyone applauded. That’s rugby, isn’t it? You get knocked down, you get up again. And yet I have to admit that I offered a silent prayer of thanks that I didn’t actually hurt the little guy. They aren’t making many kids like Toki these days; in fact they aren’t making enough kids at all.

If you want proof of the rule that nobody knows anything, look up a 1988 bestseller called Yen! Japan’s New Financial Empire and its Threat to America. It was by Daniel Burstein, an American financial journalist, and the gist was that the yen was about to supplant the dollar as the world’s reserve currency; that Japan was buying up key American assets and flexing its muscles, with a frightening martial revanchism, with a view to taking over the world. As geopolitical prophecies go, it is hard to think of anyone who has ever written such total and utter balls.

Boris Johnson collides with Toki (Photo: Getty)

Shortly after Burstein had his vision, the Japanese economy entered a decades-long stagnation, and a slo-mo collapse in population. Today there are more nappies sold for old people than there are for babies (and that is not just because they have special pervy clubs in Japan, I am told, where grown men are allowed to dress up as infants). There are more pet dogs in Japan than there are children under 15. The population is declining at a rate of about 260,000 per year. Imagine if Britain lost Wolverhampton, then Plymouth, then Bolton, then Derby… and so on. By 2050 the head count is expected to fall from 125 million to 90 million — about the same size, by then, as the United Kingdom.

And as everyone in Europe turns their avid gaze to China, and as the whole of London bids ni-hao (quite properly) to President Xi, it is all too easy to forget that this place, Japan, was once predicted to be the new superpower. It is too easy to discount Japan; easy and wrong. This is an amazing country.

I spent the first 24 hours in a state of stupefaction — partly at the lickable-pavement cleanliness of the place, and partly at the politeness. I ran by the Yodo river in Osaka, and through the town, and all the way I rejoiced as people turned and bowed with an ornate ceremony. ‘I don’t mean to be rude,’ said my private secretary when I told her, ‘but I don’t think they are doing it just for you.’ Still, they do seem to like Britain.

As the doors opened of the giant Hankyu store, I watched as female shoppers charged — like a herd of very careful wildebeest — to buy hot British scones and Scottish fish and chips and jam from Essex. And never forget Japanese investments in the UK. One Japanese car plant in Sunderland makes more cars than the whole of Italy (which says something about the disaster of the euro, of course). Japan is free, it is democratic, it has a good human rights record, it is artistically creative and it is basically aligned with western ideals. What is not to like?

They are still knocking spots off us when it comes to transport infrastructure. It is 51 years since they introduced the Shinkansen, or bullet train. Long before we have caught up, they will have built a maglev, called the Linear, which will go from Tokyo to Osaka in 40 minutes — and mainly in a tunnel. It’s like going from London to Edinburgh in about an hour. It makes HS2 look like Stephenson’s Rocket.

As for consumer goods, I test-drove two revolutionary new Japanese cars — a hydrogen-fuelled Toyota and a superb electric Mitsubishi five-seater. They are both coming to the EU market — and oh yes, what was the one question that no one bothered to ask, in three solid days of talking to Japanese business people? No one seems worried about the UK’s EU referendum. They are smart enough to know that Britain will remain, whatever happens, in a European free-trade zone.