Modern slavery: On the police beat in Manchester
The Salvation Army says it has seen nearly a fivefold rise in the number of slavery victims it has helped in England and Wales since 2012.
Det Con Colin Ward, from the modern slavery unit at Greater Manchester Police, says trafficking is "happening more than ever".
On a journey around the city, he explained to BBC reporter Mat Trewern that slaves could be found in car wash services, the construction industry and affluent households.