The raids were the result of a six-month investigation by officers across the East Midlands into human trafficking, which found 76 people, mainly men, being forced to live in cramped and overcrowded conditions and work illegally for little or no pay.

Two of the homes raided were in Viking Way, Kettering, where seven people were forced to live in three-bedroom houses, with one bathroom and were only seen by neighbours when they were leaving and returning from work.

A 50-year-old man, a 45-year-old woman and four Indian men aged 51, 29, 26 and 23, who are all from Kettering, will appear in court next month alongside seven other people from across the Midlands as a result of the huge police operation, which also uncovered a £10m money laundering scam to cover up the movement of the gang's slaves.

All of the workers were taken to safe locations and questioned by police, before some were rehomed in Kent and given legal work, with some sent back to their home countries at their own request.

Speaking shortly after the raids, Northamptonshire Police's Glyn Timmins said: "All the workers seem relieved and pleased with the police intervention.

"We are talking to them to firmly establish what happened."

Around 200 staff from agencies such as Northamptonshire Police, The UK Borders Agency and the Gangmasters Licensing Authority worked together for six months on the investigation, Operation Ruby.

Immediately after the raids, police said they believed they had smashed an international crime ring dealing with labour exploitation and had arrested eight people in connection with human trafficking and money laundering.

As well as 12 properties in Kettering, police searched another nine in areas including Market Harborough, Peterborough and Coventry as part of the operation.