Some of them really didn't know what they were coming to this country for

Lynne Chitty Social worker

But police say they are powerless to stop the trade under existing laws in the UK.

Typically the teenagers arrive in Britain with forged passports, claiming to be under 18 and wanting political asylum.

But many will have already been targeted by human traffickers in their home country, who may have used voodoo threats and violence to intimidate them.

Sussex police superintendent Dave Gaylor told the BBC's Southern Eye: "Some will disappear on the day they arrive, others have disappeared three, four months later.

"You may have three go missing at once and then none for several weeks, so it's very difficult to police and identify when they might go missing."

Voodoo ceremony

One girl was abducted at gunpoint from Hove sea front, but the majority leave quietly because they have been terrified by threats.

The head of West Sussex child asylum team, Lynne Chitty, said the traffickers forced girls to go through a voodoo ceremony before they left their home country.

"They have to swear not to tell anyone and while they are swearing they are being cut," she said.

"Some girls have 40 or 50 cuts all over their body. They are forced to drink blood and this all happens in a dark and frightening place.

We are doing everything in our power to stop this

West Sussex County Council

"One girl when she told me was just trembling, crying, saying 'my body's going to blow up and I'm going to die now'."

The traffickers promise to take the girls away from poverty but if they refuse to go to Italy, they come looking for them.

A further 41 teenagers are thought to have been brought to this country by the traffickers. They are being kept at secret locations along the south coast to protect them from the gangs.

One of the girls told Southern Eye that she will be killed if she is identified.

Sarah - not her real name - is 15 and thought she was coming to England to work in a supermarket. She wants to stay in this country and is defying the traffickers.

"I am frightened because I am going to die," she said.

Deaths

"I don't want to die. I want to stay in life."

The girls are sold on to Nigerian "madams" in the industrial towns of northern Italy, the documentary says.

There are 2,500 African prostitutes working on the streets of Turin alone. Seven have been killed in the past four years.

Marianne - not her real name - told the BBC how she shares a house with 20 other Nigerian prostitutes.

You have to be on the street as if you are not a normal human being

'Marianne' Prostitute

They sleep in shifts and are forced to work around the clock. If they refuse to work, the girls are severely punished.

"Many of our girls are dying here because of 'I cannot do it'. They organise our boys and beat you.

"You have to be on the street as if you are not a normal human being."

Marianne wants to go back to Africa, but before she can leave she has to pay her madam �34,000.

Sussex police launched an investigation into the trade over a year ago.

Detective Sergeant Andy Cummings said some of the traffickers had been identified, but said there was little officers could do because of loopholes in the law.

"Unfortunately, at this time there appears to be a loophole where there is not quite enough legislation to cover the offences we find," he said.

A West Sussex County Council spokesman said: "We are reducing the numbers who are going missing by working very closely with all the agencies, including the police. We are doing everything in our power to stop this."

People living in the BBC South region can watch the programme on Southern Eye at 1930GMT on BBC Two.