Four men have been charged with modern slavery offences after 29 people believed to be from Vietnam were found in the back of a van that was stopped on the M5 in Devon.

Police stopped the vehicle on Friday morning near Cullompton after reports that a group of people were seen getting into the back of a van after arriving on a boat.

On Sunday, four men – Frank Walling, 72, from Colne, Jon Ransom, 63, from Kent, Keith Royston Plummer, 62, from Sheerness, and Glen Martin Bennett, 55, from Burnley – were charged with human trafficking and assisting unlawful immigration to a member state. They were remanded in custody and will appear at Truro magistrates court on Monday.

Devon and Cornwall police said: “The van and another vehicle were stopped by officers on the M5 near J28 just after 9am in which 29 men, women and children were located, all believed to be Vietnamese. Police and partners continue to take care of those located in the van.”

The National Crime Agency, Border Force, Immigration Enforcement and other relevant partner agencies have been informed and are assisting police.

A spokesman for Devon Children and Families Partnership said: “The UK government will decide what the next steps will be for these individuals. In the meantime, Devon and Cornwall agencies are supporting the group, and arrangements for temporary accommodation will be made if any of the individuals are under 18 years of age, pending further decision about their status.”

A British Red Cross spokesperson said volunteers were supporting a number of people who were alleged victims of human trafficking. “We are providing them with practical and emotional support at a rest centre while the police conduct their investigations,” they said.

Nearly 200 migrant flower pickers employed at a farm raided last week have written to police demanding an apology for being made to feel like “victims”.

Three men were arrested on suspicion of modern slavery and gangmaster offences after the raid near Helston, Cornwall.

The letter, signed by 189 workers, says morale has been affected and defends the farm bosses.

Devon and Cornwall Police said it cannot comment on a live investigation.

The arrested men have since been released while investigations continue.

The majority of those employed at the Bosahan farm are from Lithuania and Romania.

Justinus Stanislaus, a Lithuanian translator who is helping the group, said: “They want to prove to the world that they are not victims of modern slavery.

“It’s a wonderful place to work and they are treated well. They refute everything that has been said in that respect”.

On the evening of the raid many of the workers gathered at Camborne Police Station to protest against the arrests.

The following day, Chief Constable Shaun Sawyer explained the raid, saying: “There were reports into police of alleged labour abuse, alleged offence of modern slavery.

“Therein lies the dilemma – you have to at some point intervene and you just sift your way through the evidence.”