Britain may have banned slavery outright since the 1830s. But the practice has hardly ended. As recently as 2017, the International Labour Organization estimated there were 40m “modern slaves” around the world.

Last week saw an official warning to UK bosses against profiting from these unfortunates. Speaking about the Chinese province of Xinjiang, the foreign secretary Dominic Raab reminded UK companies of their obligations to ensure their suppliers were not staffed by slave workers. He said the Chinese government had detained more than 1m Uighur Muslims in the province and sent many to factories as forced labour.

“Barbarism we had hoped lost to another era [is] being practised today, as we speak,” he thundered.

Unveiling new rules to curb it, he said companies would now face fines if they failed to ensure their supply chains were free of slaves. “Our aim, put simply, is that no company that profits from forced labour in Xinjiang can do business in the UK and no UK business is involved in their supply chains,” he said.

Mr Raab’s words certainly strike a different tone from that of former prime minister David Cameron’s government. The then chancellor George Osborne unblushingly downplayed human rights and spoke of a “Golden Era” between Britain and China, while pushing for inbound investment in everything from nuclear infrastructure to his pet “Northern Powerhouse” project.

But aside from the diplomatic message, it is worth considering how potent the foreign secretary’s warning was to UK bosses. And the answer is: not a whole lot.

First, let’s look at those new sanctions, which have been tacked on to the 2015 Modern Slavery Act, Theresa May’s landmark legislation that aimed to stamp out forced labour and trafficking. These will not fine companies for using slave-owning suppliers. They will fine them for not publishing a so-called “Modern Slavery Statement” prominently on their website, as all companies and public bodies with a turnover of more than £36m are supposed to do.

To fulfil that obligation, companies simply need to produce a form of words saying that they have looked into their suppliers’ practices.

Just how seriously companies take this bare-bones obligation is open to question. A 2019 review of the legislation claimed that about 40 per cent did not even bother to publish a statement. And no law presently exists to punish those companies that are found to have profited from forced labour through their supply chains, whether wittingly or not.

Even those that tick the boxes may not fully understand what goes on at their suppliers — especially in distant countries. Many rely on consultants, whose reports can vary in quality. While some are doubtless assiduous, the worry is that others may scratch the surface no more deeply than those accounts given by 1930s “fellow travellers” such as George Bernard Shaw about the joys of life in Stalin’s USSR.

An Channel 4’s Dispatches programme in 2017 found that garment makers in the English city of Leicester paid well below legal minimum wages when producing clothes for such well-known UK brands as New Look, River Island, Boohoo and Missguided. The companies’ response? The work had been subcontracted to those factories without their knowledge or consent. A 2018 investigation by the Financial Times also exposed labour exploitation in Britain’s garment industry.

The government seems to hope that it can subcontract enforcement to the City of London, with investors dumping the shares and bonds of those that do not abide by ethical standards. But there’s little sign of that working.

Last June, following a Sunday Times investigation, Boohoo again came under fire for buying from companies that did not pay minimum wages. Yet while the share price briefly halved when the story broke, it quickly recovered when it was clear Boohoo would face no real sanction, despite a critical report commissioned from a barrister, Alison Levitt QC.

Of course, it’s not just about the bankers. Consumers are also responsible. They may talk a lot about ethics. But there’s not so much enthusiasm for changes that could push up the cost of clothing or the price of the next airline flight.

The UK is, of course, right to condemn Beijing for its mistreatment of China’s Muslim minority. But simply chiding bosses yields limited returns. The government needs to give them more reason to worry about their suppliers’ labour practices. Until that happens, the gap between words and deeds will be large.