The Truro Crown Court gave Jon Ransom, 63, Glen Bennett, 55, and Frank Walling, 72, four and a half years each and Keith Plummer, 63, three years and four months.

They were charged with "assisting unlawful immigration" for their role in smuggling the Vietnamese nationals, including 17 children to Newlyn, a seaside town in Cornwall in southwestern U.K., by fishing boat in April last year, a statement from the court said.

Once in Newlyn, the Vietnamese were bundled into a windowless van to be taken to a hideout.

Police officers acted upon a tip-off, stopped the vehicle and found the Vietnamese crammed inside the back of the van.

The indictment said Walling owned the boat and had sailed it across the English Channel from France along with Bennett with the Vietnamese nationals while Plummer hired and drove the van with Ranson.

Judge Robert Longford said the defendants were "trading in human misery."

"This was a well organized, for-profit operation. In that van, being carted about like freight, were 29 living breathing, desperate human beings whose plight you cared not one jot for," he said, as cited by the court statement.

The victims have since been referred to the Home Office and social care services, the court said.

The sentencing came even as British police officers were in Vietnam to meet with families of 39 Vietnamese killed in a refrigerated container truck in Essex last October.

The two youngest victims were 15 years old and oldest was 44. Their remains were brought home in November.

The Essex police recently wrapped up post-mortems, which found the cause of death was a combination of hypoxia and hyperthermia in an enclosed space.

Vietnam is consistently one of the top source countries for modern slaves in Britain, with at least 3,187 Vietnamese victims being identified since 2009, according to official data.

Victims trafficked from Vietnam most commonly end up being exploited, often in cannabis farms and nail bars, but many are also sexually exploited, according to a report commissioned by Britain’s independent anti-slavery commissioner Kevin Hyland.