Law prof Suzanne Goldberg has a short article here explaining:
A case recently filed in the European Court of Human Rights (ECtHR), M. v the United Kingdom, shows just how vigorous and heinous the slave trade continues to be. But the trade’s character has changed, with £5 billion generated each year largely from traffickers’ control of women and children, making trafficking in persons the second largest criminal activity in the world.
M, who was forcibly transported from Uganda into the UK’s sex industry, is but one of the hundreds of thousands of women trafficked into Western Europe each year. The sheer numbers demand that states respond not only as prosecutors but also as protectors of victims. Since traffickers often force their victims to evade immigration control and violate other criminal laws, states regularly treat trafficking victims â€“ who are notoriously difficult to identify as such â€“ as illegal immigrants and criminals. As a result, victims frequently face detention, prosecution, expulsion, and destitution in the destination country.
With clearer attention to the facts and more developed identification systems, the international community has begun to see these women and children for what they are â€“ victims of severe human rights abuses.