A man has been arrested on suspicion of a modern day slavery offence after a raid at a travellers' site.
The 29-year-old was one of four people detained at the River View site on Mill Lane in Brigg, North Lincolnshire.
Two men, aged 42 and 21, have been held on suspicion of growing and supplying drugs and a woman, 49, is in custody on suspicion of money laundering.
Detectives said they seized a large amount of property on the site and were trying to identify the owners.
Warrants were executed at seven properties on the site and at a storage unit on Santon Business Park.
A number of items have been seized from the business park, Humberside Police said.
Supt Dave Hall said: "I would like to praise and thank the community of the River View site for their understanding and courtesy during today's operation. This has been a disruptive day for them, they have been very helpful and understand the need for us to target criminality."
"Today's operation is a very visible statement of our intent to protect people from criminality and exploitation which has no place in today's society."