SOCA's report The United Kingdom Threat Assessment of Serious Organised Crime says criminals exploit illegal immigrants trafficked to the UK as cheap casual labour using violence, intimidation and bondage.
Industries targeted by gangmasters include construction, horticulture, agriculture, care, hospitality and food processing.
People trying to enter the UK illegally pay anything up to $37,000 (ú20,000) to the traffickers. The debt is recovered through bonded labour. People smuggling and human trafficking is worth around $15bn a year.
SOCA was formed from the National Crime Squad, the National Criminal Intelligence Service and HM Revenue and Customs personnel in 2005.