I remember when I first read a news story about human trafficking, about 30 years ago. It was a report in the Observer and I honestly thought the paper had gone bananas. It simply couldn’t be true, could it? An actual modern-day trade in people, where they’re effectively kidnapped, brought to other countries, their papers taken from them, forced to work at dangerous jobs in terrible conditions. I really thought a conspiracy theory had the reporters in its grip.

I miss the days when it was possible to be so ignorant. So unaware of the depths of depravity to which humankind will sink if there’s a buck in it for them. From the vantage point of 2024, when there are an estimated 40 million adult and child victims of such exploitation (for labour, for sex, for both), they count as halcyon days.

So then to Slavery at Sea, an hour-long summary of a three-year investigation by the BBC into allegations of grotesque exploitation of migrant workers by a Scottish fishing fleet owned by Tom Nicholson, which he runs with his son Tom Nicholson Jr.

We meet numerous men employed by Nicholson’s company. Though you might want to put quotation marks around the word employed, as all claim to have gone virtually without pay, let alone rest periods, or health and safety protections, and all the other things deemed necessary when you are working with heavy machinery out on the already perilous sea. Their stories are very similar. Most paid fees to and signed contracts with an agencies in their native countries – the Philippines, Taiwan, Ghana and Punjab in India, as the Nicholsons apparently moved their recruitment grounds to stay ahead of the authorities once reports of abuse on their fleet started coming in. The men would arrive in Scotland to find themselves in very different jobs on different boats from the ones specified, and would have their passports and documents confiscated before they set sail.

Joel Quince, from the Philippines, counts as one of the relatively lucky ones – he at least had experience in fishing. Others were factory workers or electricians who had signed up to be engineers, to work on tankers rather than as labourers on fishing boats. But, as almost all of them point out, who did they have to complain to when the reality was different from the idea they were sold? How do you demand your rights when you are miles from land, trapped with a crew of strangers and a skipper who has caused you to breach your visa conditions and proved he does not have your best interests at heart?

The men claim they were kept short of food and water and worked to exhaustion for what amounted to a few pounds an hour. And you couldn’t simply stop, weak with hunger, or refuse to keep going through the relentless 18-hour days, because, as Quince says, “if I stop working, all my colleagues suffer”. His attitude serves as a marker of the gaping gulf in humanity between the workers and the bosses.

Stories of injuries and brushes with death abound. Erma, the widow of Indonesian worker Yoyok Wijayanti, tells of his fatal accident on a boat that shouldn’t have been at sea at all. There are tales of hardship and vulnerability: after the workers fled or were removed from their jobs in police raids, they spent years waiting for justice to be done, facing deportation and the great iron pitilessness of the system. Their main port in the storm was the local Fisherman’s Mission, run at the time by sisters Paula Daly and Karen Burston, who were among the first to become aware that something might be amiss in the way the Nicholsons ran their £4m business.

Police attempts to gather evidence and break up other operations are shown. The nugatory fine imposed on the Nicholsons’ company after they are eventually found guilty of some of the charges brought against them is noted. Reporter and presenter Chris Clements tries to question Nicholson Sr face to face at his yard. We see the white-haired figure of a man retreating deep into his office and closing the door behind him.

Nicholson’s company denies any wrongdoing, apart from delaying treatment for Quince when he suffered a head injury on a boat skippered by Nicholson Jr, to which they pleaded guilty when it came to court 10 years later – requiring them to pay him £3,000 in compensation. The rage and powerlessness felt by the men who have suffered (and by those who are trying to change the law, increase protections and help individuals) is palpable. “You favour the wealthy and don’t care about the poor,” says Quince bitterly. “It’s just an image for all of you that you have the law.”