What pays for North Korea’s nuclear programme – not to mention Kim Jong-Un’s cars, yachts, 1,000-seat luxury cinema, $1 million annual consumption of alcohol, etc? North Korea’s domestic economy can’t provide this kind of wealth. But as Panorama showed on Monday night (BBC One and iPlayer), there are other possibilities.

An estimated 100,000 North Korean workers are being employed abroad, especially in Russia and China, though “employed” is not quite the word. Almost all their money goes to their supervisors or to the North Korean government – what’s known as the “party fee” or “revolutionary fee”. They can’t say no to work, which tends to be 10 to 11 hours a day, sometimes without a break.

If you want to make any money for your family back home, the trick is to bribe your manager, who might let you take another job working nights. Most are working for their families: indeed, Pyongyang normally only gives travel permits to workers with a family, so that they’re less tempted to try and escape once abroad.

One worker on a Russian building site tells the reporters, who are posing as flat-hunters: “You’re treated like a dog here, and you have to eat trash. You have to give up being human. This is what working here means.”

This kind of investigation leaves the viewer with mixed feelings. As with the revelations about Planned Parenthood’s alleged role in distributing the organs of aborted babies, this is journalism that can only be done by unethical means – lying and secret recording. But the results are too important to be ignored. At a Polish shipyard, a local employer tells them gleefully: “They’re very hard-working. When you ask Poles, ‘Can you work weekends?’ they say ‘No chance, I have to go drinking’ and so on. But if you ask the Asians, they say, ‘No problem.’ During the day, during the night, it doesn’t matter. So we have to have them.”

Panorama says the conditions often amount to slavery, and it’s hard to think of a more accurate single word. The programme was made over two years, and in December – shortly after filming finished – the UN issued new sanctions, demanding that North Korea bring its migrant workers home. But the deadline was extended from 12 to 24 months, probably because of pressure from China (which employs about 100,000 North Korean “slaves”) and Russia (40,000).

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