RNA - There were more than 300 live policing operations currently, with cases affecting "every large town and city in the country,” the National Crime Agency said in its report.
The NCA said previous estimates of 10,000-13,000 victims in the UK were found to be the "tip of the iceberg."
“It’s likely in the tens of thousands,” the NCA's vulnerabilities director Will Kerr said. “The more we look for modern slavery the more we find evidence of the widespread abuse of the vulnerable. The growing body of evidence we are collecting points to the scale being far larger than anyone had previously thought.”
Human trafficking into modern slavery was now so widespread that ordinary people would inadvertently come into contact with victims every day, Kerr said.
Victims are predominantly from Eastern Europe, Nigeria and Vietnam, but some victims are from the UK itself, the NCA said.
The victims can be men, women or children of all ages but it is normally more prevalent among the most vulnerable, minorities or socially-excluded groups.
Human traffickers and slave masters are using the internet to lure their victims with hollow promises of education, jobs and even marriage.
The NCA warned that the key sectors for slavery now included domestic and care workers, food processing, construction, car washes, fishing and agriculture.
It said the growth in modern slavery was being driven by international gangs seeking more money by controlling people within a huge range of economic sectors, rather than just dealing drugs.
Sexual exploitation is the most common form of modern slavery reported in the UK, followed by labor exploitation, forced criminal exploitation and domestic servitude.
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