In most cases, the women were being used as 'sex slaves', after being knowingly or unknowingly led into the prostitution circuit. The women involved in raids conducted this year have so far been of Lithuanian, South Asian and Southeast Asian origin.
In the latest incident, four men and one woman were arrested this week following raids at the India Cottage restaurant in Samlesbury, Lancashire, and a house in Manchester. They have been changed with human trafficking.
Antonin Seidl, 29, from Manchester was among those charged with the trafficking of a woman for purposes of exploitation, false imprisonment and trafficking a woman within Britain. Others facing similar charges included Gabina Buzova, 29, Siraj Uddin, 38, and Mohammed Islam, 38.
Police sources say the number of women trafficked into Britain for sexual exploitation has increased rapidly in recent years. The incidence has increased after several east European countries joined the European Union in 2004.
Reports say Yorkshire has emerged as the focal point for what has been dubbed as the 'sex slave trade'. One of the worst cases involved a 15-year-old Lithuanian girl who was bought and sold numerous times after being repeatedly raped and forced to work in saunas, brothels and massage parlours up and down Britain.
The girl finally escaped the hands of her traffickers in Yorkshire after breaking down in the toilets of a Sheffield nightclub and begging for help from some local girls.
Three illegal immigrants - from Macedonia, Albania and Kosovo - were jailed for a total of 38 years for brutalising the girl in a case which the trial judge at the Sheffield Crown Court said carried "echoes of the days of slavery".
The sources say that many innocent women from other parts of the world are duped by promises of employment in London, but after arriving in Britain, are forced into the prostitution circuit. After East European countries joined the EU, it has become easier for their nationals to enter Britain.
In early February, 13 people hailing from the Indian subcontinent, China and Thailand were arrested in a swoop on a suspected brothel in north England, highlighting the problem of trafficking of women into Britain.
The Humberside Police's investigation team ran the operation codenamed Lenham after months of gathering evidence. Expert financial investigators were drafted to trace where the profits went.
Detective chief inspector Dena Fleming, the officer in charge, said after the raids: "This is an investigation into the trafficking of Asian females into the UK for the purpose of sexual exploitation".
She described the women involved as "little more than slaves".
"Typically, there could be several women in a house, mostly foreign nationals and with a lot of male callers. Usually the women do not leave the house unless accompanied by people who have some control over them."