Image copyright Thinkstock Image caption Both sides in the debate say they are motivated by protecting the human rights of sex workers

It's not often that a liberal newspaper like The Guardian rails against an organisation like Amnesty International.

But last week the paper ran a stinging editorial questioning the wisdom of the human rights group.

It said Amnesty would make a "serious mistake" if it advocated the decriminalisation of prostitution - a decision the group's international council will vote on later on Tuesday.

It's not just The Guardian that is upset. Several women's groups have got together with a host of big-name actresses - including Meryl Streep, Emma Thompson and Kate Winslet - to criticise Amnesty after a draft of its policy proposal was leaked.

Former US President Jimmy Carter has also urged Amnesty to be very careful before it changes its stance.

The arguments for decriminalisation

Amnesty's leaked proposal says decriminalisation would be "based on the human rights principle that consensual sexual conduct between adults is entitled to protection from state interference" so long as violence or child abuse or other illegal behaviour isn't involved.

Those who favour decriminalisation say it removes the stigma of prostitution and makes it easier for sex workers to go to the police if they need protection from violence.

It's also argued that it empowers prostitutes to strike open deals with their clients about safe sex. There are various groups across the world that support decriminalisation, such as Durbar in India.

Germany is one of the countries which liberalised its prostitution laws, together with New Zealand and the Netherlands.

One of the main reasons the Germans opted for legalisation in 2002 was the hope that it would professionalise the industry, giving prostitutes more access to benefits such as health insurance and pensions - just like in any other job.

Felcitas Schirow, a German brothel owner and sex worker, says the 2002 law has helped give prostitutes self-confidence.

"The owners of brothels could invest money," she says, "and the women could pick a good employer where they felt at home and who met their requirements."

Media playback is unsupported on your device Media caption Paradise Stuttgart was opened in 2008, six years after Germany legalised such facilities

Criticisms

But there are many who argue that the German experiment has gone badly wrong with very few prostitutes registering and being able to claim benefits. Above all, the number one criticism is that it's boosted sex tourism and fuelled human trafficking to meet the demand of an expanded market.

Figures on human trafficking and its relationship to prostitution are hard to establish. But one academic study looking at 150 countries argued there was a link between relaxed prostitution laws and increased trafficking rates.

Other critics of the German model point to anecdotal evidence of growing numbers of young Romanian and Bulgarian women travelling to Germany to work on the streets or even in mega-brothels.

An investigation in 2013 by Der Spiegel described how many of these women head to cities such as Cologne voluntarily but soon end up caught in a dangerous web they can't easily escape.

The Coalition Against Trafficking In Women argues that pimps would be the only ones to benefit from decriminalising prostitution.

The Nordic model

The women's groups and anti-trafficking campaigners opposing the Amnesty motion start from the premise that most prostitutes are victims who sell sex simply to survive.

They argue that human trafficking and prostitution are inextricably linked.

They think the best approach to prostitution is the "Nordic model". This is where the police go after the purchasers of sex by handing out tough fines or prison sentences to punters, and leave the sex workers in peace. In other words, the aim is to stifle demand.

It was a policy adopted by Sweden in 1999 and it's since been copied by a host of other countries including Iceland, Canada, Norway and most recently Northern Ireland.

The European Parliament wants more member countries to adopt the model.

Some MPs at Westminster also believe it should replace the confusing patchwork of laws in England and Wales (in summary: buying and selling sex isn't illegal but brothel-keeping, kerb-crawling and soliciting sex in a public place are).

What does the law say about paying for sex in the UK?

Image copyright PA

Often referred to as kerb crawling, it is illegal to approach someone in a public place to ask for their services as a prostitute

It is also illegal to persistently approach people in a public place to offer to sell them sexual services

But you are allowed to pay for sex if the person is over 18 and hasn't been forced into prostitution, apart from in Northern Ireland

Renting or allowing the use of your property as a brothel is forbidden

Is there anything wrong with selling sex?

But there are critics of the Nordic model too. Dr Jay Levy has studied the Swedish example and he's not convinced by police figures suggesting prostitution is in decline there.

Instead, he thinks the Swedes have just succeeded in pushing prostitution into more clandestine spaces, making it even more risky.

"It basically reduces safety," he says. "It reduces the amount of time that sex workers have to suss out a situation. And because clients are criminalised, they are reluctant to leave any information by which they can be traced."

Those pushing for decriminalisation inside Amnesty International and their newfound opponents both say they want to protect the human rights of prostitutes.

But there's no getting around it - they each have very different approaches about how that's best achieved.

And they can't both be right.