IN THEORY slavery was completely abolished in 1981, when Mauritania became the last country to outlaw forced labour. In practice, however, it persists in many forms, some of them surprisingly blatant. In November CNN broadcast a grainy video depicting the auction of 12 migrant Nigerian men for farm work. When human trafficking and less extreme forms of coercion are included, slavery-like practices remain disturbingly common.

Modern slavery is often seen as a problem that is limited to poor countries. However, forced labour in the developing world feeds into supply chains that lead to the West. In its 2018 report on global slavery, the Walk Free Foundation, a campaign group, examined supply chains in the G20 group of large economies. Its aim was to work out which countries use which policies against exploitation. The G20 accounts for three-quarters of global trade. However, only seven of its members have rules to lower the risk that goods and services are sourced from forced labour.

To work out which supply chains are most at risk of abuse, the report’s authors trawled through an official American list of goods produced by forced labour. They also scoured data from NGOs, academic papers and government agencies in order to catalogue the source of “at-risk” goods from countries supplying the G20. In terms of import value, the industries most affected are computers and mobile phones, clothing, fishing, cocoa and sugarcane.

Many countries present clear-cut illustrations of modern slavery. China imports $1bn-worth of coal a year from North Korea, dug out by miners who toil because of an inherited-worker status rather than out of choice (a tenth of North Korea’s population is thought to be forced to work for the state). The cotton industry in Central Asia depends on migrant labourers; in Turkmenistan tens of thousands of people are forced to pick cotton to fulfil state production quotas. India’s huge brickmaking industry in Andhra Pradesh relies on families working in bonded labour.

The United States has done the most to curb modern slavery in its supply chains. Executive orders ensure that government contractors take measures to eliminate abuses. Brazil has a “dirty list”, which publicises firms found to be using forms of modern slavery and blacklists them from public tenders. The European Union promotes socially responsible public procurement, and encourages member countries agreeing to government procurement deals in foreign countries to take local social conditions into account.

Nonetheless, such policies only work if they are enforced. And there is good reason to think that more stringent controls are needed. A survey in 2017 by the Chartered Institute of Procurement and Supply found that only 6% of managers at British firms were certain their supply chains are untainted by modern slavery.