Amid the noisy battering the North American Free Trade Agreement is taking from both Democratic presidential hopefuls, one recent statement from Hillary Clinton was particularly resonant. “We will have a very clear view of how we’re going to review Nafta,” the New York senator said. “We’re going to take out the ability of foreign companies to sue us because of what we do to protect our workers.”

The treaties and tribunals that regulate international investment have become both more powerful and more controversial as global trade becomes less about goods flowing across borders and more about multinationals siting abroad. Concern is growing not only among US presidential candidates but also among emerging market governments and development campaigners.