When the British government surveyed employment in the City of London recently, it came across a pleasingly symmetrical fact. About one-third of the high-skilled workers were foreigners and so were about one-third of the low-skilled workers.

This knowledge that foreign workers are critical to the most dynamic sector of the economy has not stopped Gordon Brown, the prime minister, from growling about “British jobs for British workers”. Across the developed world, politicians such as Mr Brown are responding to public fears about high levels of immigration. In Italy last week, police backed by bulldozers swept through settlements of Romanian immigrants. In the US, Hillary Clinton recently made the first false step in her formidable presidential election campaign by sounding soft on illegal immigration.

Some anti-immigration activists think we are now reaching a tipping point in both western Europe and north America. Immigration is becoming such a hot political issue that politicians will be forced to clamp down. The period of high migration will come to a close.

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