The country was shocked when 39 people were found suffocated in the back of a lorry on an industrial park in Essex last October. The discovery that the victims were economic migrants sparked a conversation about the scale of human trafficking in the UK. Vietnamese people are among the most trafficked people in Britain and many of those smuggled here end up in modern slavery; working on cannabis farms, in brothels and nail bars.

In this episode we speak to investigative reporter Cat McShane, who introduces us to Ba, a teenager captured, tortured and forced to work in a cannabis farm in the north of England. We also speak to the Guardian’s Amelia Gentleman, who tells us about her experience of going on a police raid of a suspected illegal nail bar.

Producers: Lucy Hancock and Duncan Barber