Overview: As President Trump and the North Korean leader, Kim Jong-un, prepare for an unprecedented summit, Panorama investigates North Korean modern-day slavery. It is thought that more than one hundred thousand North Korean workers are posted abroad to earn money for the cash-strapped regime - money that is being ploughed into Kim Jong-un's nuclear weapons programme. An international consortium of journalists has filmed undercover to reveal secret work gangs operating in Russia, China and Poland.