THERESA May has been in New York to address a special summit at the United Nations on refugees and migrants, held with the aim of “bringing together countries behind a more humane and co-ordinated approach”.

At least that is what the official agenda says, but it did not seem to interest the Prime Minister much. Her speech concentrated on how to stop refugees and migrants coming, or at least to prevent them getting where they want to go. Their ultimate destination is usually one of the wealthier parts of Europe, the UK or Germany or Scandinavia.

She wants such places to be out of bounds to them. “We should help ensure that refugees claim asylum in the first safe country they reach, and embed this as a principle”, she said in her speech. “The current trend of onward movement benefits criminal gangs, endangers people and reduces the prospects of refugees ever returning home to rebuild their countries. So we must do far more to support the first safe countries themselves, assisting the refugees and host communities, an approach that is starting to work in Jordan, Lebanon and Turkey.”

In other words, for heaven’s sake keep them out of Europe! But Europe is where many of those with resources enough to make it have already arrived. Or else they are left waiting forlornly on the Greek islands, in the Macedonian mountains, halfway over the Serbian passes or in front of the barbed-wire fences put up by Hungary and Slovenia. Still, these are relatively (all things being relative) the lucky ones. They are the sort of Syrians who can speak English, even quote Shakespeare, evidently educated people. You should watch a short film, a piece of cinéma vérité, about the thousands of them who last summer, before the barriers came down, set out to walk from Budapest to the Austrian border. It is hard not to feel moved. The film is on Youtube: We Walk Together, by John Lokotos.

By contrast, the refugees who have fetched up in the refugee camps of Jordan, Lebanon and Turkey are rather the poorest of the poor and the weakest of the weak, who could never have paid to get to Europe and certainly were not capable of walking there. In their plight they receive some international charity, but have no right to employment or any other rights. This must be Theresa May’s definition of “an approach that is starting to work”.

Even her subservient BBC allowed itself a show of sorrow for these waifs and wretches in a recent programme on the refugee camp of Zaatari, a ramshackle collection of containers, tents and rusting pipes in the middle of the desert a few miles beyond the Syrian border, which they had crossed to escape massacre by President Assad or by Islamic State. Zaatari houses 80,000 people, and 11 babies are born there every week. It is difficult to imagine them “returning home to rebuild their countries” any time soon. So Zaatari is where Theresa May wants them to stay.

The distinction between economic migrants and refugees is one she is especially keen on. Refugees are presumably those driven from their homes by violence or mortal danger and so deserving of humanitarian help, at least at arm’s length.

What is the difference between them and economic migrants? It must be that the economic migrants left their homes not under duress but of their own free will, propelled perhaps by nothing more than a normal human desire to escape a dead end and make something of themselves and their lives.

I would have said this was a motivation a Conservative Prime Minister might easily be able to understand. It has driven multitudes of her own people, in the past out to colonise an empire and even in the post-imperial present to seek their fortune in California or Hong Kong, or indeed in Europe, where more than a million of them live, if perhaps not for much longer. The nations of the British Isles are full of footloose folk, certainly the Scots and Irish, even the English too. Once they might have gone away because they were poor or starving or oppressed, but now they are economic migrants. They leave to fulfil their own ambitions, but this is also one of the main ways they have collectively benefited humanity, spreading their abilities and their energies in societies that can make better use of them. Apparently, according to Theresa May, the process does not operate the other way round.

Yet for the life of me, I fail to see how economic migrants can be labelled as inherently a bad thing. OK, we should keep them out if they have criminal records or some horrible disease, we should limit the trail of dependents they bring with them and we are entitled to prefer those with skills we reckon we require. But the pressures of economic migration on a host country are one index of its prosperity. That is why the most powerful nation in the world, the US, is basically a nation of economic migrants, or of the descendants of economic migrants. With interruptions, it has been booming since the mid-nineteenth century, and it has successfully kept its borders open but controlled.

By definition, after all, economic migrants want to work. They go to the US to work and they come to the UK to work. The Prime Minister must know this because in 2010 she was the Home Secretary who took it on herself to limit net immigration to 100,000 a year. She failed to hit the target in 2010, and she failed in every single subsequent year. At this moment, some limited progress she had made in the interim is going into reverse, with the result that in 2015 the UK took in 333,000 immigrants. Now as head of the Government, Theresa May will in this respect continue to fail.

Why has her policy been such a failure? It is because the forces that drive migration are economic forces, not to be controlled by political action that flies in the face of them. The UK remains a rich country, but its native population no longer has much taste for some of the hard graft that once helped to make it so, manual labour for the men or industrial drudgery for the women. This native population is anyway in numerical decline, because a vital margin itself emigrates and because otherwise it is no longer able to reproduce itself as in the days of its vigour. So how are all the existing jobs, let alone any new jobs, to be filled? Immigration is the only answer there can be.

Economic migrants have to wrench themselves out of their own societies and set off into the unknown, so they are usually young, active and brave. They are not only pulled by the prospect of a better life but also pushed by the poverty they leave behind: it is an old economic adage that countries which cannot export their goods will export their people. As a last resort, they will cram into the backs of lorries or on flimsy boats even at the risk, too often fulfilled, of death. Human beings of such sterling qualities would be an asset anywhere, including here. We should let them come: if England does not want them there is more than enough room in Scotland.

Finally I cannot close this column without congratulating my friend Ian Blackford MP and sending my best wishes for the future to the Brain family of Dingwall who he saved from deportation by his unstinting efforts. Nothing better illustrated the heartless irrationality of the immigrant policy that marks the main contribution to date in British politics of Theresa May.