'Human trafficking almost sounds like it is just moving people across borders, but it's really modern-day slavery,' the group's director of awareness and prevention, Laila Mickelwait, told a businesswomen's luncheon yesterday. 'It is the exploitation of a person's vulnerabilities.'

The United Nations said this month that 2.4 million people are victims of human trafficking at any one time, and 80 per cent are exploited as sex slaves.

And in 2007, the US State Department marked Hong Kong as a transit point and destination for people trafficked for sexual exploitation and forced labour, although the government received a top rating for enforcement of anti-trafficking laws.

Mickelwait is seeking to persuade legislators all over the world to criminalise the purchase of sex - a measure first implemented in Sweden 10 years ago - instead of prosecuting prostitutes, which she says would stamp out the demand for sex and drive out organised crime.

Sweden now has the lowest rate of human trafficking in the European Union.

The documentary takes the viewer first to Eastern Europe, where girls - many of them orphans - are tricked or kidnapped into forced prostitution where they are 'broken' by brainwashing, heavy drugs and repeated rape and abuse from their owners until they become so obedient that there is no need for chains.

The women are then sent to cities to work as prostitutes, many to centres like Amsterdam where prostitution is legal and slavery can slip under the radar.

Closer to home, the setting shifts to Cambodia, where there is a thriving child sex trade, with parents often complicit in selling their daughters.

In one enlightening scene, an aid worker in Cambodia who runs a recovery home for former slaves says money and education are not the solution because it is not the poorest parents who sell their daughters but those who want money to buy an expensive appliance. 'It is a moral and spiritual issue,' he said.

Mickelwait addresses the argument that legalised prostitution protects sex workers, such as in Singapore where prostitutes in registered brothels have regular health checks.

'When you are implementing health checks on women, are these checks being made on the men? It can take a month to get results, and these women are servicing 30 to 40 men a day, so these tests aren't reliable anyway,' she says. 'They are physically and psychologically tortured. It is not a legitimate job option and shouldn't be treated as one.'

Former prostitutes, traffickers and clients speak frankly in the documentary about their experiences, shattering the perceptions that prostitution is just like any other job, or that the women enjoy it. One former prostitute describes it as the greatest acting job.

The film screens only at UA Windsor today and tomorrow. A DVD can be bought on the website of Exodus Cry, a Christian organisation that is building recovery homes called LightHouses for former prostitutes in Moldova and is inviting donations.