CNN's Laura Perez Maestro contributed to this report.
London (CNN) -- British investigators were questioning suspects Monday after police rescued 24 men that they said were kept as slaves -- some for as long as 15 years.
Police in Bedfordshire, northwest of London, arrested five suspects under a new anti-slavery law passed last year, alleging that they lured the men to a trailer park with promises of food and shelter, then threatened them with violence and forced them into hard labor.
The men, from England and parts of Eastern Europe, are "all believed to be victims of slavery," police said. Living in squalid conditions in the town of Leighton Buzzard, many of the men were on the verge of starvation, police said.
"There's no electricity. There's no running water. People haven't had their hair cut. (They're) wearing dirty clothing. And made to perform labor, rather than being given proper food and proper wages for their labors," said Detective Chief Inspector Sean O'Neil of Bedfordshire Police.
Tips from other alleged victims who had managed to escape the site led to a lengthy investigation that culminated in Sunday's raid, police said.
Bedfordshire Police issued a statement Monday saying that four of the five people in custody were being questioned. The fifth is a woman who "is pregnant and has been released on police bail and will be questioned further following the birth of her child which is imminent," the statement said.
Police identified the four men arrested as three brothers -- James Connors, 23, Tommy Connors, 26, and Patrick Connors, 19 -- and their brother-in-law, James Conner, 33. The four are scheduled for a court hearing Tuesday morning and will be held in custody until that hearing, police said.
Nine of the men rescued in the raid have left a medical reception and "have chosen not to support the police investigation," Bedfordshire Police said in the statement Monday.
"Those people who we continue to help are appreciative of the support that is on offer, but it will take some time to work through with them what has happened," O'Neil said in a statement.
Investigators are searching for two additional suspects, Bedfordshire Police said.
According to the United Kingdom Human Trafficking Centre, which assisted Bedfordshire Police in Sunday's operation, nearly 1,500 cases of slavery and human trafficking have been reported to British police in the past two years.
A new anti-slavery law passed last year in Britain means that anyone convicted of holding a person in servitude can spend up to 14 years in prison.