What should be the response of high-income countries to the pressure for immigration of unskilled workers from poor countries? A visitor to the US will quickly discover that this is today's hottest topic. It is equally contentious in Europe.

That there should be pressure for immigration of unskilled people into high-income countries is hardly surprising, given the huge wage gaps. The number of illegal immigrants in the US, predominantly from Mexico, is estimated at 11m, up from 4m in 1992. Illegal immigrants make up about 5 per cent of the labour force, but 24 per cent of people working in farming, fishery and forestry, 17 per cent of cleaners, 14 per cent of construction workers and 12 per cent of workers in food preparation.