Migrants try to recover after clashes with the police during a protest at the Lesvos Port on September 6, 2015, as they demand to be transferred immediately to Athens. More than 230,000 refugees and migrants arrived in Greece by sea this year, a huge rise from 17,500 in the same period in 2014, deputy shipping minister Nikos Zois said on September 3. AFP PHOTO / ANGELOS TZORTZINIS Image Credit: AFP

When the crew of HMS Bulwark first fished immigrants out of the Mediterranean, they were expecting to find the world’s hungry, wretched and destitute.

Instead, they found them relatively healthy, well-dressed and carrying mobile phones and credit cards, which they intended to use upon arrival in Italy. The military learnt then what politicians are only slowly beginning to work out — that this is not simply a refugee crisis. The world’s poor are on the move because they’re not quite so poor as they used to be, and can afford to travel.

A great migration has begun, and it could be with us for decades. The photographs of the body of Aylan Kurdi, a three-year-old Syrian boy, vividly convey the human tragedy on Europe’s borders — but not the complexity. Many are fleeing war, but many are fleeing poverty. The Royal Navy found a pregnant Nigerian woman who had paid $1,200 (Dh4,400) for the journey and a father from Faisalabad, an industrial city in Pakistan.

Under European rules, they would be judged by whether they were fleeing war or poverty — but the distinction seems moot. All were prepared to risk death to give their families a better life; seeking only the right to start at the very bottom. This Great Migration was not expected because, for years, politicians believed that there would be less of it as poor countries became richer.

Give aid, not shelter, ran the argument.

“As the benefits of economic growth are spread in Mexico,” Bill Clinton once assured Americans, “there will be less illegal immigration because more Mexicans will be able to support their children by staying home.”

When Jose Manuel Barroso led the European Commission, he made the same argument: only third world development will tackle the “root causes” of the problem. In fact, the reverse is true. Never has there been less global hardship; since Clinton’s day, the share of the population in extreme poverty (surviving on less than $1.25 a day) has halved. Never has there been less violence: the Syrian conflict is an exception in a period of history where war has waned. It might not feel like it, but the world is more prosperous and peaceful than at any time in human history — yet the number of emigrants stands at a record high.

But there is no paradox. As more people have the money to move, more are doing so — and at extraordinary personal risk.

So the Great Migration is a side effect of perhaps the greatest success of our times: the collapse in global poverty. The Washington-based Centre for Global Development recently set this out, in a study drawing on more than a thousand national censuses over five decades. When a poor country becomes richer, its emigration rate rises until it becomes as wealthy as Albania or Armenia are today. This process usually takes decades, and only afterwards does wealth subdue emigration. War is a catalyst. If conflict strikes, and the country isn’t quite as poor as it once was, more of those affected now have the means to cross the world.

The digital age means they also have the information. When the world was poorer, Europe could be pretty relaxed about immigration laws. The British Nationality Act of 1948 declared that all 600 million of the King’s subjects had the right to settle in Britain — which, today, seems like lunacy. But then, no one cared: very few of those subjects had the means (or inclination) to migrate to our cold, depopulating island.

Even after shocks like the partition of India, which claimed a million souls and displaced at least 10 times as many, Britain was not deluged with immigration applications. In 1951, we signed the UN Refugee Convention promising to shelter anyone with a “well-founded fear of persecution”. Wars kept being waged, but newcomers arrived at the rate of 100 a day.

Now, they’re arriving at the rate of 1,500 a day. Globalisation has transformed the global movement of people, as well as goods and money — and Britain handles this perhaps better than any country in Europe. We are one of the few countries in the world where unemployment rates for immigrants are no higher than for natives, and where there is no far-Right party causing havoc in Parliament. We impose fairly tough rules (we even deport Frenchmen who don’t work) but Britain is now the most successful melting pot in Europe.

The countries currently urging us to take on more asylum seekers are, by and large, the same ones who are in crisis after accepting more than they have been able to handle. If you misjudge the refugee crisis, you incubate a political crisis: this is the lesson that David Cameron has learnt. Efforts intended to help can end up causing harm, costing more lives.

Since the Italian navy decided to send rescue missions to the Mediterranean, the number of people making the crossing (and perishing) has trebled. Doubtless Angela Merkel meant well when she invited every Syrian to apply for asylum in Germany. But she will be toasted by the new breed of people traffickers, who will now have far more families to extort and leave stranded in Budapest or pack into boats on the coast of Libya.

A photograph of a drowned child is heartbreaking, but should not change policy: a botched response can lead to many more dead children. Hundreds of Yemeni children will likely starve this winter, victims of its civil war — we won’t see the pictures, so we’re unlikely to see anyone petitioning Parliament about them. But it’s no less of a tragedy. There is, of course, more that Britain could and should do for Syrians; even taking 10,000, as Yvette Cooper suggests, is manageable for a country that absorbs this number of immigrants every week. But let’s not pretend our doing so will help the rest of Syria’s four million registered refugees.

The Great Migration is a 21st-century problem, far bigger than Syria and bigger than the authorities in Brussels seem able to comprehend. To panic now, as Merkel is doing, will just bring more to panic about. The solutions of the last century — refugee camps, or the notion that you can stem the flow of migrants with foreign aid — need to be abandoned, and a new agenda needs to be forged. Europe, in short, needs to begin a new conversation. Given that David Cameron is one of the few people in Europe keeping his head throughout this crisis, he’s the ideal man to start it.

The Telegraph Group Limited, London 2015