As parliament has now passed the Modern Slavery Bill, it's time to say well done to those who have campaigned for years to get human trafficking on the political agenda.

The Bill, which was first announced by the government in November 2013, aims to consolidate existing trafficking offences and introduces harsher sentences for traffickers. It also establishes an independent anti-slavery commissioner and includes recommendations for supporting trafficking victims, although the lack of emphasis on victims is one aspect that has drawn significant criticism. A similar law in Northern Ireland, for example, has made victim support mandatory rather than recommended.

Human trafficking has been a prominent issue among Christians for a number of years. Organisations such as Stop the Traffik and Tearfund have played a major role in informing and mobilising the Church, and there are many others working to combat modern slavery in a number of ways, of which legislative change is just a part.

A key campaign issue for Stop the Traffik is getting companies to ensure that their supply chains do not use trafficked workers, and an amendment has been added to the Bill make sure that company reports had to indicate whether their supply chain was 'slavery free'.

But although the Bill is a step in the right direction, the relationship between trafficking and prostitution is one issue that has been totally side-stepped.

"For some reason there's a reluctance, including among well-meaning charities and NGOs that work in trafficking, to put these two issues together," says Labour MP Gavin Shuker, who chairs the all-party parliamentary group on prostitution and the global sex trade. "It's viewed as too politically contentious. They just want a nice piece of legislation on the statute book.

"It's all too much of a cosy stitch up... So while the Modern Slavery Bill needs to go through and it contains some decent measures, its complete silence on the issue of prostitution is an act of cowardice," Shuker said, ahead of the parliament passing the Bill.

Lord McColl, who is the vice-chair of the all-party group on prostitution, tabled an amendment to the Bill to criminalise the purchase of sexual services at the end of last year, but it wasn't adopted.

Christian organisation CARE has worked on this Bill with a number of Peers, and is frustrated by the failure to include this amendment – essentially clamping down on traffickers but not tackling the root of the problem. "Overwhelmingly the evidence suggests this is a highly effective means of addressing the root cause of trafficking, namely demand for sexual services," says Louise Gleich, CARE's human trafficking and sexual exploitation policy officer.

While the Church has played a fundamental role in bringing the issue of human trafficking to the fore, we may also be responsible for letting prostitution slip off the agenda – an industry which involves approximately 80,000 people in the UK, most of them women.

"The Church is the reason why the issue of human trafficking has the prominence that it now does," says Shuker. "If you look at the move over the last decade... it's incredible. But trafficking appears nice and straight forward: you've got the good guys and the bad guys. Prostitution is much more complex."

The two issues are clearly interlinked. Of all possible victims of trafficking in the UK in 2013, 42 per cent ended up working in the sex trade. The percentage of those trafficked who end up in the sex trade is higher among women. According to a report for the National Crime Agency, 62 per cent of women trafficked to the UK will end up working in the sex industry. (The number of men trafficked into labour is proportionately higher than women.) In Europe, at least 70 per cent of trafficked people end up in prostitution.

There is a danger that if Christians say anything about prostitution or try to act against it, it's seen as a moral crusade. It can be caricatured by critics who think that Christians have something against sex or that they are trying to impose their own moral code on society.

But Shuker says the moral imperative to combat the global sex trade isn't just a Christian view: "I'm a Christian, it shapes my view of human dignity first and foremost but I'm working with people from every belief and of none... I think that good law is law that protects the most people and promotes human flourishing, and I think I would probably think that regardless of my faith."

Nonetheless, a reticence in the Church to talking about prostitution – or the way we talk about it when we do – may not be doing us any favours. Charlotte Gibb, an outreach volunteer who campaigns on the global sex trade, says: "We don't talk about it – if we do it's in the context of outreach or seeing it as an issue: 'We need to do something about for these vulnerable women.' We're not very good at talking about the demand side of it and linking it together.

"People see trafficking as a terrible violation, but people associate prostitution with choice. Even at church we prefer to talk about outreach as anti-trafficking work, when really we're what we're doing is visiting prostitutes. But you say that word and people flinch," says Gibb.

Christian feminist Natalie Collins says that the Church has fought trafficking because of the redemption narrative it depicts. "In sex trafficking you have the perfect victim: totally powerless, abused and then rescued; that's a narrative where that person has no agency. People don't see prostitution as so clean and pure."

The 'Swedish model'

Legislating on such issues is an unenviable task – not least because people claim that opposite policy options have achieved the same result, namely, protecting those working in the sex industry.

When Shuker became chair of the all-party group on prostitution he thought that the current law was sufficient, but possibly needed to be enforced better. Four years later, he says he's changed his mind, and that the law on prostitution, which includes five different Acts over a 50-year period is "completely deficient". "It doesn't even know what it's trying to achieve," he says.

Currently English law does not ban prostitution, but there a number of laws which make certain activities illegal, such as purchasing sex from someone who has been pimped or trafficked, introduced by the Policing and Crime Act in 2009.

In 1999 Sweden implemented a law which criminalised the purchase of sex but not the sale of sex. This means that the person who pays a prostitute could be arrested, but the prostitute wouldn't be. Variations of the so-called 'Swedish model' have subsequently been implemented in Norway, Iceland, Canada, France and Northern Ireland's new law on human trafficking also includes a ban on the purchase of sex. The European Parliament also officially supported the principle in February last year, after British Labour MEP Mary Honeyball proposed a report on the issue.

Proponents say that the Swedish model helps tackle trafficking into the global sex trade by reducing both the supply of and the demand for prostitution. It is thought that countries which have tougher laws on prostitution are less likely to become a haven for traffickers. It just won't be worth their effort – or so they hope.

Norway criminalised the purchase of sex in 2009. Five years on, the results of a new government-commissioned study published in October, suggested that it had become a less inviting place for prostitution, and, by implication, sex trafficking. The report, which was the product of six months of research and evaluation, said that Norway had seen a decline in prostitution, and had not seen a rise in violence against sex workers, as opponents had feared.

Those supporting this form of legislation also point to the rise of prostitution in other European countries where prostitution is legal, such as Germany and the Netherlands. Germany legalised prostitution in 2002 and is now home to Europe's only mega-brothels, and has had an influx of sex workers from Eastern Europe.

But there are at least two sides to every argument, and this is no exception. Liberal feminists would say that prostitution is just like any other job, and should be recognised as such. Radical feminists, however, say that prostitution, which is predominantly done by women, subordinates women to men and puts them at risk of great harm. Some Christians align themselves with this view, but others would also add that prostitution goes against God's vision for human sexuality.

The argument that prostitution is like any other service industry tends to concentrate on workers' rights, equality and encouraging safe practices. There is vocal opposition to any attempt to reduce prostitution from groups such as the English Collective of Prostitutes, who argue that the majority of prostitutes have chosen their line of work, not been forced into it.

A study by The Economist last year assessed the effect of the shift to online – for both 'service' advertisement and gathering information about prospective clients. The report analysed the hourly rate of prostitutes from major cities around the world comparing the potential earning power based on physique, geographical location and services offered. The magazine argued that the move online would increase the safety for escorts and prostitutes – allowing more user-ratings and feedback on forums.

While many will disagree with The Economist's premise, we would do well to consider the conclusions they reach. The magazine argues that the consensus on following the Swedish model is "misguided" and overlooks the complexities of the issue. It says that sex will always sell and that criminalising its purchase will not affect demand and will instead increase the risk to sex workers.

Many on this side of the debate point to the decriminalisation of prostitution in New Zealand in 2003 which was done to promote the health and safety of sex workers. The argument is that if the purchase of sex is criminalised, it will push the industry underground, prostitutes won't be able to do thorough checks on clients which would place them at greater risk. They would also be reticent to report acts of violence or health concerns – increasing the likelihood of violence and sexually transmitted diseases. Similarly, those purchasing sex will not report anyone who they believe to have been trafficked. However, opponents to this policy point to the increase in prostitution on New Zealand's streets after the change in the law.

Annie Lobert, the founder of Hookers for Jesus, who worked in the US sex industry for 16 years, contests the view of prostitution as any other service. "It harms you emotionally, physical, mentally and behaviourally," says Lobert. "Does waitressing do that?

"Having a bunch of sex partners, it's just like pornography – they're ingrained in your memory and you get flashbacks because they're touching an intimate place that only one person should have a right to touch," Lobert adds.

"You can't sell love. It doesn't work. If we could it would be the fountain of youth. A lot of the men that would buy us were trying to buy the relationship – they were lonely men."

An equality issue

Unusually, Christians may find themselves more aligned with radical feminists on this issue, who argue that prostitution is an example of male exploitation of women.

The End Demand campaign was launched by a number of women's charities and trade unions in October last year. The campaign calls for the introduction of a Sex Buyer law in England and Wales, and seeks to see the issue on the political agenda following the upcoming election.

The campaign highlights that half of women in prostitution were paid for sex acts before the age of 18, which makes prostitution closely linked to child sexual exploitation. More than half of women involved in prostitution in the UK have been raped or sexually assaulted, with the majority of these acts committed by sex buyers. Another prominent factor is drug addiction – according to the Home Office, 95 per cent of street prostitutes in the UK are 'problematic drug users' (either dependent or recreational).

"For me a genuinely gender equal world is one without prostitution," says Shuker. "Anyone who has a genuine concern for the most vulnerable in our society has to look at look at the sex trade and ask basic questions about whether the law works and whether it protects the most vulnerable... Whichever framework you want to look at it through, there needs to be change."

Collins agrees with the need to see prostitution from the basis of equality. "A lot of people wouldn't see the sex industry related to women not having as many opportunities to lead as men," she says. "[But] there is a direct link between gender stereotyping and prostitution... it's all part of the spectrum of inequality.

"In a society where we are commodifying human beings, we are reducing their humanity. We also reduce the [meaning] attached to sex – it's not about a partnership of people who care about each other. Even outside of a Christian perspective, it's been reduced to a transaction," Collins says.

Some Christians might say that it's a good idea to criminalise the purchase of sex, but to decriminalise the sale of sex suggests that we're condoning it. But Gibb disagrees: "If we do that, then we are still saying that the women involved are treated as criminals. As Christians we do believe that there's a better way for those women, and we wouldn't want to condone it, but we need to recognise that in a lot of circumstances they are victims – anyone could have ended up there but for the grace of God, I think we have a duty in law to recognise that."

Collins challenges the Church to think about how we consider success in this area. "What does life in all its fullness mean for someone in engaging in prostitution? Coming to church and becoming a nice family woman?" she asks. "If our model of success is only when they do what we want them to do, it is manipulative in itself. What about if that person is walking towards a different element of freedom in their lives, and able to do it safely?"

But it isn't only that the sex industry objectifies women. Lobert says that while she was working as a call girl, she and her fellow prostitutes would objectify the men they served. "I used the men as much as I could," she says.

Lobert feels the Church needs to be involved in teaching men and women what their bodies are designed for. "We're not designed to be an abuser, purchaser or abused," she says.

"We need to have churches that are able to say the way our culture objectifies women is not acceptable," says Gibb. "The Bible's vision for women and for men is so much better."

What Christians can do

The Modern Slavery Bill doesn't do everything we might like it to, but many consider it a real step forward in recognising the prevalent evil of human trafficking around the world. It also shows the influence that Christians can have when they work to expose something that needs to change. Would this Bill have come about without Christians campaigning on it? Perhaps not.

When it comes to prostitution, things are different. There isn't the same consensus among Christians, and there is a danger that what we do say will be discredited as mere moralising.

If our argument is a moral one – that we believe in the dignity of every person, that they are made in the image of God, and not to be prostituted for the gratification of others – then we need to demonstrate that we may be moralists, but we are not squeamish.

So for Christians who do want to campaign on this issue, we do ourselves no favours if we're not specific. There are some prostitutes who choose to work in the sex industry free from financial obligation as well as physical or psychological compulsion. Equally, there is a likely majority who do not. But if we are to give them a voice, we want to make sure we have the best possible chance of being heard.

Shuker says it's important that Christians have an opinion on this subject that isn't limited to "militant Christianity", but instead a more nuanced understanding of the issues involved – particularly that those involved in the sex industry often have very chaotic lives.

But he also says it's important that Christians do take a stand. "We should get angry about this. If there are tens of thousands of women being exploited day in day out on the streets of our cities and towns and no one cares, that's exactly were the Church needs to be."

Some might say, therefore, that we don't want to reduce prostitution in Britain because we'd rather not see it on our streets, but because there are millions of people around the world who cannot free themselves from an industry that endlessly devalues and abuses. And because it says something very wrong about our society if people are able to buy each other in the guise of sexual liberation.

The recognition that people are exploited around the world is what has motivated action on modern slavery. The ongoing fight, and what the End Demand campaign seeks to demonstrate, is that the best way to tackle that exploitation is to target the demand for sexual services.