Four residents of a caravan site have been arrested on suspicion of slavery offences, police said.
Three men and one woman were held following a long-running investigation by Bedfordshire Police which suggested a number of people were being held against their will - some for as long as 15 years - in poor conditions at the site, and forced to work for no pay.
Around 100 officers were involved in the operation at 5.30am at the Greenacre caravan site in Leighton Buzzard.
Some 24 men, all believed to be victims of slavery, were taken from the site to a medical centre. Police said they were mostly from English and eastern European backgrounds.
Detective Chief Inspector Sean O'Neil, from the Bedfordshire and Hertfordshire major crime unit, said: "The men we found at the site were in a poor state of physical health and the conditions they were living in were shockingly filthy and cramped.
"We believe that some of them had been living and working there in a state of virtual slavery, some for just a few weeks and others for up to 15 years.
"Because of the number of victims and suspects and the size of the site, we needed the assistance of many officers from specialist units today. We are aware the operation has caused a lot of disruption to the other residents of the site and we thank them for their co-operation and understanding."
Anyone with information about what has been happening at the site is asked to contact police on 01707 355798, or Crimestoppers anonymously on 0800 555 111.