This government’s obsession with outsourcing public services to the private sector has led to some catastrophic failures.

The idea that outsourcing public services is of positive benefit to the taxpayer by driving up standards and providing value for money has been a central precept. But there has never been a shred of evidence that outsourcing has achieved either of these objectives.

Indeed, there are many examples of how it has failed – the collapse of Carillion is of course the most recent. But there have also been instances of human rights abuses at the hands of firms contracted to run immigration detention centres; overcharging for contracts; and as with the case of security for the London 2012 Olympics, failure to deliver what was promised. I could go on.

But the latest revelations about government outsourcing are of a different scale altogether. S ome 40 per cent of the government’s top 100 suppliers are not compliant with their legal obligations to prevent modern slavery.

Those who are forced to live in conditions of slavery can be told they have to work off fabricated “debts”, are frequently trafficked across borders or have to provide forced labour. For women, who make up the majority of those in slavery, it is also frequently characterised by sexual violence or being forced into prostitution.

Modern slavery is a defining crime of the 21st century. The UN has reported that it is the second-largest criminal industry in the world, and the criminals organising this forced labour profit by about $150bn. There are as many as 40 million victims of modern slavery across the globe. And this is not simply a problem for developing countries: there are between 10,000 and 13,000 victims of modern slavery in the UK.

My colleagues on the Labour frontbench, Diane Abbott and Kate Osamor, have done excellent work on how we can stop this crisis at home and abroad. Yet to do this properly, we must also examine how government procurement might be propping up modern slavery too.

Taxpayers’ money should not be used to bankroll human rights abuses. Exploitation arising from lax procurement would undermine the ethos of service that lies at the heart of the public sector. It would also offend common decency.

The government must be especially vigilant on this issue. Many of their top suppliers operate in sectors where the risk of slavery is higher, such as construction and infrastructure. There is also a higher risk with firms that operate with large, complex and less accountable supply chains, which is often characteristic of the type of firms the government contracts with.

They typically involve huge amounts of subcontracting and the frequent use of low-waged temporary or agency workers, performing low-skilled or manual tasks. Moreover, many of these workers are migrants, who are particularly vulnerable to modern slavery.

This is why firms have an obligation to investigate their supply chains, protect their workers and train their staff properly, and why the government must make sure companies are actually doing this.

It is galling that four out of every 10 of their biggest suppliers have been criticised for failing to meet the requirements the Modern Slavery Act sets out, including shortcomings in analysing their supply chains, poor or unactioned policies or lack of proper training.

In the past, Labour has criticised the government for buying from firms that aren’t tax compliant, fail to recognise unions or to pay their workers poverty wages. But this is a failure of a different scale.

That’s why a Labour government would not stand by if firms remained non-compliant with their obligations under the Modern Slavery Act. We will reserve the right to re-tender a contract or to bring it back in-house if a firm isn’t compliant with the legislation. It is a condition of basic human decency that we won’t work with firms that could be complicit in the oppression of millions.

But we will also go further by ending the presumption in favour of outsourcing and putting a stop to the dogma that “private profit is always best”. Labour will offer a new vision that ends the rip off of taxpayers and in which public services are run for the many, and not the private interests of the few.

Jon Trickett is shadow minister for the cabinet office and MP for Hemsworth.

@jon_trickett