Twenty-four "slaves" who were held at a caravan site in filthy and cramped conditions for up to 15 years have been freed as part of an ongoing police operation.
Officers were searching for more victims and suspects last night after making five arrests under anti-slavery laws in a dawn raid.
The arrests at the Greenacre caravan site in Leighton Buzzard, Bedfordshire, formed part of a two-year operation. Weapons, drugs and money were also found at the site.
Detective Chief Inspector Sean O'Neil said the men were recruited from soup kitchens and benefits offices. "They're told, if you come here we'll pay you £80 [$155] a day and give you board and lodgings. But when they get here, their hair is cut off them, they're kept in some cases [in] horseboxes, dog kennels and old caravans, made to work for no money, given very, very small amounts of food."
They were made to work as labourers on projects across Britain and even in Scandinavia, detectives said. Slavery was outlawed in Britain more than 200 years ago.
Anti-slavery campaigners say that, at any one time, around 5000 people in the country are victims of trafficking for forced labour and prostitution.
Paul Donohoe, a spokesman for Anti-Slavery International, said: "Coercion is used to bring people into the country to work in the sex industry or do other types of forced labour.
"Some are told they are coming to work in a cafe and only find out they are being exploited when they arrive. Others are paid a nominal wage, from which is deducted money they are told they owe; most commonly they are told they are paying back the cost of transporting them to Britain."
More than 200 officers were involved in yesterday's raid. Five residents of the caravan site, four men and one woman, were arrested under the Slavery and Servitude Act 2010. The slaves, all men, were taken to a medical reception centre. Some were said to be English and others eastern European.
O'Neil said: "The men ... 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 ... up to 15 years.
"Some people did leave and told us what was going on and when we looked back since 2008 we were aware of 28 people who had made similar accusations."
* More slaves in Britain come from Nigeria than from any other country and more than a quarter are men and children.
* Official figures compiled using the National Referral Mechanism - the Serious Organised Crime Agency's framework for identifying victims of human trafficking - show that, between April 1, 2009 and March 31, 2011, 1481 people were working as slaves in Britain.
* Campaigners say that is only the number found by police.