Natasha was 18 when she decided she wanted to leave Latvia and study in the UK. She was working at a local cafe and saving up when one of her mother's friends said she could get her work in London as a nanny. She spoke to the family over the telephone and they arranged for her flights and to collect her at the airport.

When she arrived, she was taken to a flat by a man called Alex. There she was raped and forced to become a prostitute. She was a prisoner and he made it clear he knew how to find her family.

Within three months she was sold on to a man called Dimitri for £3000, who drove her to Glasgow. Dimitri would drop Natasha off and collect her from brothels in the city. He would call her throughout the day to check how many clients she had. She was not allowed to go out alone. Once, he beat her so badly she couldn't leave the house for weeks.

When the brothel was raided by police, initially she told officers she was there out of choice, fearing what could happen to her grandmother. In time, she told them what had really happened.

Natasha is one of an estimated four million people trafficked across the world every year. Officials estimate that some 500,000 people are trafficked in Europe alone; most are women and girls who are forced into prostitution from countries such as Albania and Russia.

Scotland is certainly not immune. In the past four months officers have rescued some 30 women under an operation codenamed Pentameter II. Women from countries as diverse as Latvia and China are thought to have been brought here against their will or under false pretences.

Some Chinese women pay Snakehead gangs - so named as the people they smuggle are often referred to in Chinese as "man-snakes" - up to £20,000 in return for what they believe will be legitimate work opportunities in the UK only to discover they have been bonded into prostitution when they arrive.

"People trafficking is a modern-day slave trade, so that 200 years after trading in slaves became illegal it is not only still with us but is actually thriving," said John Watson, programme director for Amnesty International in Scotland.

"People who have been trafficked have all their basic human rights abused. Held against their will, forced to work and subjected to cruel and inhumane treatment. When found they must be treated with compassion, as the victims of a great injustice, rather than as criminals or illegal immigrants."

Figures from Pentameter II imply that it is also a growing problem in Scotland.

In a debate on human trafficking last month SNP MP Pete Wishart told the House of Commons Scotland had a particular problem. "The police say that the number of incidents seems to be rising more quickly in Scotland than in the rest of the UK," he said.

Tara, the recently formed Trafficking Awareness Raising Alliance in Glasgow, has reported there has been a "growing phenomenon" since 2002 of women being trafficked into the city. Senior officers say it is difficult to ascertain whether the problem is more prevalent now or new multi-agency practices mean it is better policed.

One of the problems in identifying the crime is that the women who have been trafficked are often too afraid to speak about it or stand up in court because of the threats they and their family may face in their home country.

Detective Chief Superintendent Campbell Corrigan, chairman of the Scottish Human Trafficking Group and one of the lead officers for Pentameter II in Scotland, said: " Very often we find the women who have been trafficked don't speak at all because of the threats or bonded debt involving their extended family. We want to ask the public to look out for any suspicious behaviour, such as large numbers of men entering and leaving premises such as a private flat at strange hours of the day."