Officers from Northamptonshire Police swooped on a leek farm in Lincolnshire yesterday to rescue more than 60 immigrants who had been forced to work for unlicensed gangmasters for little or no wages.

The group – aged between 15 and 67 – were made to live in substandard and unsafe accommodation, with as many as 20 people sharing two-bedroom flats in Kettering, the West Midlands and Peterborough.

Eight people local to Kettering have been arrested in the culmination of a six-month operation run by Northamptonshire Police, the UK Border Agency and several other agencies, the largest trafficking crackdown ever to be launched in the UK.

But Det Supt Glyn Timmins, director of investigations at the force, said this gang was unlikely to be the only people trafficking operation of its kind in the county.

He said: "If this is happening in one area it is very likely to be happening elsewhere and it would be impossible to say this is the only case of trafficking in the county.

"Northamptonshire is a rural area and this gang trafficked these workers specifically for farm work.

"Many of the people involved simply do not know their rights and they have been forced to pay for their passage into the country.

"They then may have their passports taken away, they are forced to pay rent.

"We are in the very early stages of the investigation and other criminality may yet be discovered, but this is serious crime. It is organised crime."

Operation Ruby – the name given to the investigation into the Kettering gang – was launched following a tip-off six months ago. Northamptonshire Police has been praised for its handling of the investigation.

Ian Livsey, chief executive of the Gangmasters Licensing Authority, said: "I want to thank Northamptonshire Police for leading this incredibly complex operation and the outstanding job the force has done.

"We hope this will be used as a template for all future investigations into trafficking into the UK.

"But I also want to make a direct appeal to farmers to use only licensed gangmasters. If they do not they are breaking the law.

"Northamptonshire has an agricultural economy, which is likely to draw unlicensed gangmasters to this area."

Labour MP for Northampton North, Sally Keeble, added: "Trafficking is a huge, huge problem and this was part of a much larger issue in the county.

"Northamptonshire has historically had jobs to attract people to the area, and there has always been a good supply of affordable housing for the gangmasters to put people up in.

"The police should be commended for conducting this investigation."