British police have charged four men with allegedly holding 24 men in slavery in what one officer calls shockingly filthy and cramped conditions.

Police arrested the suspects north of London Sunday. They are charged with conspiracy to hold people in servitude and requiring them to carry out forced labor. A pregnant woman arrested with the four was freed on bail.

Authorities brought the 24 alleged slaves to a hospital. Some were in poor health. Police say they are mostly of English and eastern European backgrounds. Some of the men had been held for as long as 15 years.

Police say they were forced to live in horse trailers and dog kennels – and were given no money and very little food. They say the suspects threatened to beat up the captives if they tried to get away. It is unclear what kind of work the men were made to do.

Police believe the suspects lured the men from soup kitchens and government welfare offices.