of customers in California, America’s most populous state.

The action follows a Guardian investigation in 2014 that tracked the complex prawn supply chain and reports by the UN and non-governmental organisations, including the Environmental Justice Foundation, that human trafficking for forced labour and slavery have become endemic in the Thai fishing sector.

The investigation established that large numbers of men who were bought and sold like animals and held against their will on fishing boats off Thailand were integral to the production of farmed prawns (commonly called shrimp in the US) sold in leading supermarkets around the world, including the top four global retailers: Walmart, Carrefour, Costco and Tesco.

The investigation found that the world’s largest prawn farmer, the Thailand-based Charoen Pokphand (CP) Foods, was buying fishmeal, which it feeds toplay on people’s fears”.

The London Mayor joked that he “shouldn’t really get involved in the American elections”, but added: “I hope the best candidate wins – I’m sure she will”, repeating his endorsement of Hillary Clinton which he first made in Chicago last week.

Building Inclusive Cities: Mayor Bill de Blasio in conversation with London Mayor Sadiq Khan at LaGuardia Community College in Long Island City. Posted by Mayor Bill de Blasio on Sunday, 18 September 2016

The two left-wing mayors, of London and New York, were speaking at an event called ‘Building Progressive, Inclusive Cities’ in New York. It is the second time the men have met, after coming together before at the Labour party conference in Britain last year.

Earlier on Sunday, Mr. Khan had spoken at a “meeting