A record number of people have been arrested
Police say 167 victims, including 12 children, have been rescued in a major crackdown on human trafficking.
More than 500 people were arrested in the operation, which involved 55 police forces in England, Wales and Scotland.
The six-month operation targeted the sale of women and children for prostitution and forced labour.
But the Home Office said police were struggling to look after the victims of trafficking, as many did not trust the authorities and refused to cooperate.
The Home Office said Operation Pentameter Two was the most successful effort of its kind.
The majority of victims rescued originated from China, south-east Asia and Eastern Europe, 13 were children, the youngest aged 14.
Women captured by human traffickers can be forced to have sex with up to 40 men a day by violent pimps, police said.
Home Secretary Jacqui Smith said: "Human trafficking is a despicable crime, perpetrated by organised criminal gangs whose business is to make money from human misery.
"Pentameter Two has been a great success. I would commend all those involved who have made a real impact in rescuing victims and bringing to justice those who exploit them."
But Home Office Minister Vernon Coaker said about half of the victims had refused to cooperate with the authorities.
He said short of "locking them up" it was difficult to know what to do.
The problem was worse among child victims who were told by those exploiting them that it was not in their best interests to co-operate.
So far 31 victims have returned voluntarily to their home countries and 17 have been removed.
Police said about 80 people had been charged as part of Pentameter Two out of 528 arrests.
They also said there was a trend emerging in which ordinary suburban houses and other residential flats and apartments were increasingly being used as brothels.