Gwent Police say the investigation was prompted by the discovery of a 43 year old man living at the Marshfield site who had been reported missing thirteen years ago.
A force spokesperson said evidence had suggested people were being kept in poor conditions at the Marshfield site and forced to work for no pay.
A man "of Eastern European origin", whose age is unknown, has been taken for medical treatment.
Since then a specialist team of detectives has been investigating and gathering intelligence to ascertain whether this part of a larger criminal conspiracy.
In addition to the suspected offences in relation to Slavery and Servitude, we are also acting on intelligence which suggests that the body of an unknown person may be buried at the Marshfield site.
As such specially trained officers, equipment and a forensic archaeologist have been deployed to investigate this.
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A dry night with clear spells for most, especially towards the north where it will become rather chilly with some mist patches possible.
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