Criminal gangs are using witchcraft spells to force vulnerable African women and girls as young as 15 to work in British and European brothels.
Traffickers lure their victims into rituals in which samples of their blood, teeth, hair and nail clippings are mixed with other "magical" ingredients, according to former prostitutes ensnared by witchcraft.
Victims are told the rituals will protect them on their way to a better life in Britain. They are later forced into prostitution and told the spells will kill them if they try to escape.
They may also be threatened that breaking the witchcraft oaths will make spirits harm members of their families. The practice is "juju", a form of voodoo black magic in Nigeria, where such rituals still exert strong influence.
Dr Michael Korzinski, a counsellor with the Helen Bamber Foundation, a charity helping victims of torture, said: "This is a lethal combination of criminal networks and so-called juju priests."
The charity, funded entirely by donations, has dealt with about 30 women who say they were subjected to juju curses.
"The girl's own bodily fluids, her pubic hair and nail shavings are used," said Korzinski. "A whole variety of things are used to create this potion that they are then forced to drink or spread on their bodies. It can happen in the country of origin and it can happen in the UK."
Last week Sara, 24, a Nigerian victim, said a trafficker had promised to take her to Europe and get her a job when she was 19: "He took me to the juju man before we went. He was in a smelly hut in the outskirts of Lagos and wearing a red cloak.
"He cut me with a razor blade on my back and on my breasts and took my blood. He cut my hair from my head and also from my armpits."
The trafficker told her she would be reunited with her body parts once she had repaid the debt she incurred in being taken to Europe. He warned that if she returned to Nigeria before doing so she would die and her spirit would be cast into hell.
Korzinski said: "People here in the West do not understand the power these belief systems have over people like Sara." Only after counselling and the blessings of a Church of England priest did Sara begin to believe that her curse had been lifted.
Another victim of traffickers was Mary, now 32, a Nigerian who was brought to Britain in 2005. Speaking last week at the Poppy Project, a charity for trafficked women, she told how she had been targeted by traffickers when she sought sanctuary at a church in Lagos after her husband threatened to kill her.
In a bid to secure her a new life abroad, the church obtained a £1,000 loan from a local money lender as a down-payment on the £3,000 the traffickers said it would cost to secure Mary a job as a domestic servant in England.
A devout Christian, she remains deeply upset at owing the money. "I will never be able to repay it," she said, covering her face with her hands.
After she arrived in Britain she was forced into prostitution at a brothel near Hove in East Sussex. "They made me drink juju water before the men would arrive," she said of the daily routine of clients visiting the house she was imprisoned in for two years.
She said she was banned from talking to her customers. "I wasn't allowed to speak to them. Once I tried to escape by stealing the keys from while she was sleeping. But she woke up and beat me."
The madam used a Bible to inflict such a savage beating that Mary lost her hearing in one ear: "There was blood everywhere that day. It was gushing from my ear."
Evidence that juju rituals were being used by criminal gangs smuggling people from Nigeria into Britain first came to light during a horrific case in 2001, when the mutilated remains of a young African boy who became known as Adam were pulled from the Thames.
Adam's throat had been slit, his head, arms and legs cut off and his body drained of blood before his torso was dumped in the river. The ritual killing was linked to a voodoo trafficking ring. One trafficker was found to have kept dozens of bottles with hair and other soft body parts in them.
Will O'Reilly, the detective in charge of the Adam case, said: "The use of voodoo in the mistaken belief that it will protect criminal enterprises is taken seriously by detectives in the UK."
The Poppy Project estimates that up to 10,000 victims of human trafficking live in the UK. It says women and children from Nigeria are the single biggest group. About 1.2m people are trafficked each year - an estimated 120,000 into Europe alone.
Mary is one of the lucky ones. She escaped after her brothel keeper fled to America. In April she was reunited with her sons - aged 12 and 9 - who have come to live with her in England. She has been granted refugee status and hopes to become a British citizen.