A 42-year-old woman from Penhow has been arrested as part of a slavery investigation by Gwent Police.

More than 100 officers and staff were involved in the execution of three warrants at addresses in Penhow, Cardiff and the Marshfield area of Newport.

A 66-year-old man and a 42-year-old, both from the Marshfield area, and a 36-year-old man from the Cardiff area have also been arrested.

The investigation began when a 43-year-old man was found to be living at the Marshfield site in very poor conditions having been reported missing by his family 13 years ago.

A specialist team of detectives has been investigating and gathering intelligence to ascertain whether this is part of a larger criminal conspiracy.

Uniform officers and detectives from Gwent Police, working with other specialist units including members of the dog section, air support unit, and the armed response unit have entered premises in relation to offences regarding Slavery and Servitude from the Criminal Law Act 1977 and the Coroners and Justice Act 2009.

Specialist officers, equipment and a Forensic Archaeologist have also resumed the search for a body which may have been buried at the site.

The four arrested are in police custody assisting officers with their enquiries.

A dedicated team of detectives has been responsible for the bringing the long-running investigation to this latest phase, which has centred around evidence and intelligence suggesting that people were being kept in poor conditions at the Marshfield site and forced to work for no pay.

A man has been taken from the Marshfield site to an undisclosed medical reception centre, where his physical and mental condition can be assessed by specialist staff.

The man, whose age is unknown at this time, is of Eastern European origin. He is believed to be a Polish national and is currently being supported by specialist officers and British Red Cross personnel.

Detective Superintendent Paul Griffiths, who is leading the investigation, which is known as Operation Imperial, said: "The action is the latest phase of a long running investigation into alleged offences of Slavery and Servitude.

"Because of the scale of the investigation we are fully aware the operation has caused disruption to other residents, especially in the Marshfield area, and we thank them for their continued co-operation and understanding.

"The offences that are being investigated are extremely serious and we would urge anyone with any information which could assist the team to contact Gwent Police on 101 quoting log 66 23/09/13.

"As a result of the publicity generated by the police activity I'm grateful to the people who have contacted us with information which is assisting our enquiry.

"Importantly we've received a number of calls from individuals who may also be potential victims or important witnesses.

"I'm urging those individuals, to contact the investigation team again by ringing our dedicated number as we believe they may have more information which could be of assistance.

"Any information can be provided in complete confidence and officers and staff can provide any appropriate support. In addition, I'm making a personal appeal to the author of an anonymous letter which was sent to a neighbouring force some months ago to contact us.

"The letter contains information which may be vital to this investigation and we need that person to contact us using the dedicated investigation number 01633 647174."

Gwent Police is working in conjunction with Serious Organised Crime Agency (SOCA), other Forces, UK Human Trafficking Centre, RSPCA and the Red Cross.