The UK Government predicts that the 2012 London Olympics could become a magnet for human traffickers, bringing in prostitutes and illegal workers.
The Home Office has unveiled plans to combat gangs which imprison women and force them into the sex trade, and push men into forced labour, the BBC reports.
The UK will allow freed victims to stay for at least 30 days for counselling.
Police Minister Vernon Coaker said human trafficking was "a form of modern-day slavery".
The Home Office's action plan states: "There is little doubt that there will be many who will seek to prosper from the Olympics being held in London.
"Hospitality, catering and construction workers will be required. Criminal elements are expected to exploit the situation by establishing themselves in London from now on."
An influx of young male sports fans, such as happened during the 2006 World Cup in Germany, could see a rise in demand for prostitutes, it adds.
Last year, church officials in Germany campaigned against human trafficking in the run-up to the World Cup, amid fears of a massive rise in forced prostitution during the event.
The Government has signed a European convention giving human trafficking victims more time to recover from their ordeal before deciding whether to help police.
The latest Home Office figures, from 2003, suggest at least 4,000 women from abroad have been forced into prostitution in the UK.
Mr Coaker said: "Frankly it brings tears to your eyes. It simply cannot carry on."
