Police raided the unnamed Harborough business as well as 21 homes in Kettering where it is believed migrant workers were living in conditions that were overcrowded and potentially unsafe.

Northamptonshire Police, Kettering Borough Council and Northamptonshire Fire and Rescue Service executed the search warrants yesterday (Tues, Nov 18).

More than 60 men and women aged between 15 and 67, from countries across Eastern Europe, including Poland and Lithuania, who were picking leeks in field near Holbeach in South Lincolnshire as part of an organised gang, have been taken back to Kettering where they are being treated as potential witnesses and victims.

More than 200 staff from nine organisations were involved, and three men have been arrested in a field in South Lincolnshire on suspicion of human trafficking.

A further four men and one woman were arrested during the raids on Kettering and in Harborough.

Those arrested have been taken into custody at Kettering and Wellingborough on suspicion of people trafficking and money laundering.

The investigation – called Operation Ruby – centres on allegations that people were recruited through advertisements and agencies in Eastern Europe and travelled to the UK on the promise of work.

When they arrived, it is believed their documents were taken from them and much of the wages they earned was withheld to pay for their housing and transport costs.

Northamptonshire Police director of investigations Detective Superintendent Glyn Timmins co-ordinated today's operation.

He said it was the culmination of months of liaison, investigation and planning involving these many agencies.

He said: "This has been a co-ordinated, large scale operation as part of an investigation into the activities of what we believe is an organised crime group that has exploited people as cheap labour in fields across this region.

"The fact that so many organisations have come together to act in this way is a demonstration of how seriously we take our responsibility to support people who have been exploited in this way and to disrupt this unacceptable activity."

Luke Hodson, of Northamptonshire Fire and Rescue Service, said: "Inter-agency action such as this is vital and today's operation could be one of the most valuable life-saving pieces of work we carry out between now and Christmas.

"This has been a huge undertaking for us and none of the agencies would have been able to take this action independently."

John Conway, head of housing at Kettering Borough Council, said: "The council has been, and will continue to work, closely with the police throughout this operation."