Without migrants some businesses, especially farming, could have become more productive through mechanisation.

ECONOMIST: Migration

Migrants without an urban hukou spend 30% less than otherwise similar urban residents, according to research by Binkai Chen of the Central University of Finance and Economics, Ming Lu of Fudan University and Ninghua Zhong of Hong Kong University of Science and Technology.

ECONOMIST: Chinese consumption is about much more than shopping

The number of visas issued to skilled non-EU migrants without job offers - known as tier 1 - would be cut by 13, 000 to 1, 000, and the corresponding number of visas issued to those with job offers - known as tier 2 - would increase by 7, 000 to 20, 700, Mrs May explained.

BBC: May unveils plan to reduce non-EU immigration

Italy has drawn criticism for handing over to Libya migrants it intercepts at sea, without screening them first.

BBC: MEPs call for better treatment of refugees by Libya

But it would do nothing for (or, as they would surely put it, against) would-be migrants ready to cross the long and largely unpatrolled border without papers.

ECONOMIST: Bolivia

Without it, cities that have attracted lots of well-educated domestic migrants would have seized up, becoming top-heavy with university graduates.

ECONOMIST: The Americano dream