I see Germans frolicking in the delicious fresh water of the Wannsee, and Germans having meticulously organised picnics on the largest inland beach in Europe; German girls smoking roll-ups and handing round punnets of strawberries, and ancient German men, nut-brown, doing creaking callisthenics in the sun. The sky is blue and the foliage of the oaks so lush that the shade is almost black; and in an ecstasy of enthusiasm for the amazing city of Berlin I raise my glass, again, and think of my grandfathers. They both fought the Germans, you see, and I don’t think they would much mind me mentioning it now. In both of their cases, the experience was pretty awful. One grandfather was forced to crash-land his plane in Cornwall, with bad results for himself and his crew. The other man — on my mother’s side — saw his best friend drown when his destroyer was cut in two in the Mediterranean. For the rest of his life my maternal grandfather had a paramount piece of advice for the world. If we wanted peace, if we wanted happiness, then there was one thing we had to avoid.

“Whatever we do,” he used to tell me, “we must stop the Germans reuniting.” He wanted to keep Germany divided in two manageable chunks — East and West. This man was no Colonel Blimp. He was no foaming xenophobe: on the contrary, he was President of the Commission of the European Court of Human Rights, and yet he believed, on the principle of induction, that Germany could not be trusted. They did it in 1914; they did it in 1939; and given the slightest chance, he believed, they would do it again.

Two decades after unification, we have taken advantage of cheap air travel to show the kids the capital of a united Germany — the heart of what is by far the most important economic power in Europe — and I have to say that my learned grandfather has been proved wrong. Everything tells me that his anxieties were baseless, and that the reunification of Germany has been one of the greatest success stories of modern geopolitics. I look around modern Berlin, and I don’t see Prussian revanchism. I see not the slightest sign of German militarism; I haven’t noticed anyone clicking their heels or restraining their arms from performing a Strangelovian fascist salute. I see a culture so generally cool and herbivorous that the bicycle is king. I see a paradise for cyclists, where the helmetless hordes weave and wobble over the wide and tree-lined roads, and a Mercedes supercar with a flashy vignet Duitsland will wait deferentially for a family to wander past his purring snout. The most serious public order problem at the moment is the tendency of Berliners to pursue the logic of their Freikörpeskultur by actually fornicating in their many magnificent parks; and such is the climate of political correctness that they decided to means-test the fines. So if you are caught in flagrante in the bushes, and you have a job, you get fined 150 euros — but only 34 euros if you are unemployed. If that isn’t broad-mindedness, I don’t know what is.

You ride around Berlin, and it doesn’t feel like the new imperial capital. There is no swagger, no pomp. Indeed, there isn’t even that much bustle — unlike London, Berlin’s population seems mysteriously to have declined over the last few years. It isn’t a global cosmopolis; it isn’t a magnet for immigrants; it’s still suffering the ill-effects of its location in what was the middle of communist East Germany.

But the Berliners seem to be young and hip, drawn to what is obviously a pretty groovy nightlife, and many of them seem to be British. In fact, if I were in my twenties and had been ordered to leave London, I think Berlin would be the first place I would choose. The rents are cheap, the food comes in proper Germanic helpings and everywhere there are bright people with tattoos engaged in start-ups. You look at Berliners today, and you ask yourself what the fuss was about, 24 years ago. There were people like my grandfather, and Margaret Thatcher, who were instinctively hostile to German unification — because they remembered what Berlin had done in two world wars. Then there were the euro-federalists, who argued that Germany needed to be “locked in” to Europe. We needed a single currency to “contain” Germany, they claimed, to “tie them in” — as though the Germans were loose cannon rolling about the European quarterdeck, about to crush innocent little Slavic nations. What a load of bunk that turned out to be.

We don’t need to “lock in” Germany with the single currency or indeed any other federalist fiction. The thing has been a disaster for the non-German parts of the EU, and the euro is now causing such pain in the periphery that even German exports are being damaged. It wasn’t the euro, I am afraid, that cured the Germans of militarism.

You look around Berlin and what hits you is how much of the city was pulverised. There is scarcely a pre-war building that does not have the scars of Russian shells or Allied bombing. This is a city that was at the centre of Europe’s two worst bouts of psychosis – fascism and then communism: an extended trauma that left Germany transformed.

I can understand why my grandfather’s generation felt as it did, but it is emphatically time to forget all that and embrace the new Germany. We have much to learn and to understand. How is it that respectable men and women can think it right to take their clothes off in the equivalent of Hyde Park? Why do they clap like Italians when their planes land? Why are they so good at making cars and machine tools? We have a great deal to admire and to copy, not least their treatment of cyclists.

We have absolutely nothing to fear.