V ietnamese smugglers call it the “CO2” route: a poorly ventilated, oxygen-deficient trip across the English Channel in shipping containers or trailers piled high with pallets of merchandise, the last leg of a perilous, 6,000-mile trek across Asia and into Western Europe.

Compared to the other path – the “VIP route,” with its brief hotel stay and seat in a truck driver’s cab – the trip in a stuffy container can be brutal for what some Vietnamese refer to as “box people,” successors to the “boat people” who left after the Vietnam War ended in 1975.

Vietnamese migrants often wait for months in roadside camps in northern France before being sneaked into a truck trailer. Snakeheads, as the smugglers are known, beat men and sexually assault women, aid groups, lawyers and the migrants themselves say. People cocoon themselves in aluminium bags and endure hours in refrigerated units to reduce the risk of detection.

As dangerous as the last leg of the migrant journey to Britain often is, those petrifying hours in a trailer are sometimes only a sliver of months if not years of harsh treatment – first at the hands of organised trafficking gangs, and then under imperious bosses at nail salons and cannabis factories in Britain.

39 bodies found in lorry container in Essex Show all 15 1 /15 39 bodies found in lorry container in Essex 39 bodies found in lorry container in Essex Thirty-nine bodies have been found in a lorry container in Essex, police have said PA 39 bodies found in lorry container in Essex The discovery of 38 adults and one teenager was made at an industrial estate in Thurrock Reuter TV 39 bodies found in lorry container in Essex Police said they believed the lorry had come from Bulgaria and entered the UK at Holyhead, in Wales, on Saturday. Getty 39 bodies found in lorry container in Essex Essex Police said it had launched a murder investigation after its officers were called to Waterglade Industrial Park, in Grays, in the early hours of Wednesday morning Reuter TV 39 bodies found in lorry container in Essex A 25-year-old-man from Northern Ireland has been arrested on suspicion of murder PA 39 bodies found in lorry container in Essex In a statement, Chief Superintendent Andrew Mariner said: “This is a tragic incident where a large number of people have lost their lives. Our enquiries are ongoing to establish what has happened. “We are in the process of identifying the victims, however I anticipate that this could be a lengthy process. Reuter TV 39 bodies found in lorry container in Essex THURROCK, ENGLAND - OCTOBER 23: Police stand near the site where 39 bodies were discovered in the back of a lorry on October 23, 2019 in Thurrock, England. The lorry was discovered early Wednesday morning in Waterglade Industrial Park on Eastern Avenue in the town of Grays. Authorities said they believed the lorry originated in Bulgaria and entered the country at Holyhead on October 19. The suspected driver was arrested in connection with the investigation. (Photo by Leon Neal/Getty Images) Leon Neal Getty 39 bodies found in lorry container in Essex THURROCK, ENGLAND - OCTOBER 23: A Police forensic investigation team are parked near the site where 39 bodies were discovered in the back of a lorry on October 23, 2019 in Thurrock, England. The lorry was discovered early Wednesday morning in Waterglade Industrial Park on Eastern Avenue in the town of Grays. Authorities said they believed the lorry originated in Bulgaria and entered the country at Holyhead on October 19. The suspected driver was arrested in connection with the investigation. (Photo by Leon Neal/Getty Images) Leon Neal Getty 39 bodies found in lorry container in Essex Police activity at the Waterglade Industrial Park in Grays, Essex, after 39 bodies were found inside a lorry container on the industrial estate. PA Photo. Picture date: Wednesday October 23, 2019. Early indications suggest there 38 are adults and one teenager, police said. The lorry is from Bulgaria and entered the country at Holyhead, North Wales, one of the main port for ferries from Ireland. See PA story POLICE Container. Photo credit should read: Stefan Rousseau/PA Wire Stefan Rousseau PA 39 bodies found in lorry container in Essex THURROCK, ENGLAND - OCTOBER 23: A Police forensic investigation team are parked near the site where 39 bodies were discovered in the back of a lorry on October 23, 2019 in Thurrock, England. The lorry was discovered early Wednesday morning in Waterglade Industrial Park on Eastern Avenue in the town of Grays. Authorities said they believed the lorry originated in Bulgaria and entered the country at Holyhead on October 19. The suspected driver was arrested in connection with the investigation. (Photo by Leon Neal/Getty Images) Leon Neal Getty 39 bodies found in lorry container in Essex Thurrock deaths: 39 bodies found in lorry container in Essex Reuter TV Reuter TV 39 bodies found in lorry container in Essex Police activity at the Waterglade Industrial Park in Grays, Essex, after 39 bodies were found inside a lorry container on the industrial estate. PA Photo. Picture date: Wednesday October 23, 2019. Early indications suggest there 38 are adults and one teenager, police said. The lorry is from Bulgaria and entered the country at Holyhead, North Wales, one of the main port for ferries from Ireland. See PA story POLICE Container. Photo credit should read: Aaron Chown/PA Wire Aaron Chown PA 39 bodies found in lorry container in Essex Police cordon at the road leading to the Waterglade Industrial Park in Grays, Essex, after 39 bodies were found inside a lorry container on the industrial estate. PA Photo. Picture date: Wednesday October 23, 2019. Early indications suggest there 38 are adults and one teenager, police said. The lorry is from Bulgaria and entered the country at Holyhead, North Wales, one of the main port for ferries from Ireland. See PA story POLICE Container. Photo credit should read: Stefan Rousseau/PA Wire Stefan Rousseau PA 39 bodies found in lorry container in Essex Police officers are seen at the scene where bodies were discovered in a lorry container, in Grays, Essex, Britain October 23, 2019. REUTERS/Hannah McKay HANNAH MCKAY Reuters 39 bodies found in lorry container in Essex Police officers are seen at the scene where bodies were discovered in a lorry container, in Grays, Essex, Britain October 23, 2019. REUTERS/Hannah McKay HANNAH MCKAY Reuters

But still they come, an estimated 18,000 Vietnamese paying smugglers for the journey to Europe every year at prices between £8,000 and £40,000.

In Britain, where Brexit has discouraged the flow of labour from Eastern Europe, migrants see a country thirsty for low-wage workers, paying easily five times what they could earn at home and free of the onerous identity checks that make other European countries inhospitable.

Vietnamese smugglers, for the most part, get their clients across to France and the Netherlands, where other gangs, often Kurdish and Albanian, or, as in the recent case, apparently Irish or Northern Irish, finish the job.

Many come from Ha Tinh and Nghe An, two impoverished provinces in north-central Vietnam, and leave for Britain with their eyes wide open to the risks, analysts say. Having watched their neighbours suddenly refurbish their homes with pricier materials, or buy better cars, they crave the same sense of security for their family, whatever it might cost them.

You have to borrow a lot of money for this journey . . . Now, it’s hopeless — nothing Reverend Simon Thang Duc Nguyen, Catholic priest in east London who emigrated after the Vietnam War

But when Britain fails to deliver on that promise, migrants can end up in a dreadful limbo, kept from seeking help by the country’s harsh immigration system and living in the grip of a shadowy system of traffickers and the employers who rely on them.

“I always encourage them, ‘Stay at home,’” the Reverend Simon Thang Duc Nguyen, the parish priest at a Catholic church in east London attended by many migrant parishioners, said this week. “Even though you are poor, you have your life. Here, you have money, but you lose your life.”

Not all the 20,000 to 35,000 undocumented Vietnamese migrants estimated to be living in Britain have horror stories to tell. Many migrants, some experts say, put up with the travails of working in Britain for the real chance of a payday.

“My research has shown stories of migrants are not all about exploitation and not all about being trafficked,” said Tamsin Barber, a lecturer at Oxford Brookes University. “People are usually coming here agreeing to take high risks to work illegally and potentially earn large amounts of money in the cannabis trade.”

But more vulnerable Vietnamese are also being trafficked to Britain, with the authorities receiving five times as many referrals last year as in 2012.

Once family and friends have scraped together enough money, the odyssey may begin with a trip to China to pick up forged travel documents. That is how many of the dozens of people who died in the truck began their journey, said Anthony Dang Huu Nam, a Catholic priest serving a church in the town of Yen Thanh, where he said dozens of the victims were from.

On the way from China to Russia to Western Europe, one of the most punishing stretches is the walk through Belarusian forests to the Polish border. In a 2017 French survey of Vietnamese migrants, a man identified as Anh, 24, told researchers that he and five other men, led by a smuggler, were repeatedly arrested in Belarus, only to be released at the Russian border to try again. When they finally succeeded, they were met by a truck waiting on the Polish side.

Catholic priest Anthony Dang Huu Nam held a mass prayer for victims at his church in Vietnam (Reuters)

“We were cold,” the survey quoted him as saying. “We didn’t eat anything for two days. We drank water from melted snow.”

Smugglers often keep people in the dark about where they are as a way of exerting total control. In a 2017 case, 16 Vietnamese people picked up by the Ukrainian authorities in Odessa thought they were in France.

When migrants disobey their smugglers, the blowback can be fierce.

“They cannot be discovered by the police, so they have to keep the discipline,” said Mr Nguyen, the priest in London. “If you do not behave, you can be punished by beatings, or for women be abused sexually.”

And once they arrive in Britain, they are often in for a rude awakening. Sulaiha Ali, a human rights lawyer, said migrants were sometimes promised legitimate work in a restaurant or on a construction site, only to be forced to work as “gardeners” in a house converted into illegal cannabis growing operations. Locked inside the house for days at a time and often living 15 to a room, workers face the risk of fire from tampered electrical wiring and health problems from noxious chemicals.

In the nail salons where many Vietnamese find work, salon bosses can control every aspect of workers’ lives, a power that can breed exploitation, though researchers said some bosses also become migrants’ surrogate parents, cooking for them and providing a place to stay.

When the police raid places housing migrants, they can often ignore signs of forced work or human trafficking and send migrants into deportation proceedings instead, migrant advocates say. “The emphasis, as soon as it’s established someone doesn’t have any identification documents, is not trying to establish whether they’ve been exploited,” Ms Ali said. “It’s on, ‘Can we justify detention? Can we get them removed back to their countries?’”

That threat of deportation, whatever someone’s circumstances, is a cudgel for trafficking gangs to keep migrants under their sway.

“There’s a serious distrust of authorities, a lot of the time because traffickers have embedded that in victims’ minds: ‘You don’t have official documents,’ or, ‘You’re going to be deported or imprisoned,’” said Firoza Saiyed, a human rights lawyer. “It’s another thing that makes disclosure really difficult.”

Older Vietnamese migrants in Britain, many of whom arrived after the Vietnam War, are separated by a wide cultural gulf from the newer arrivals, but they have still proved to be a crucial support, ever more so in the last week.

Mr Nguyen, who left Vietnam in 1984, said he had been fielding calls from families in Vietnam, wanting to know if he could tell them whether their children were in the trailer.

“The mother, the father, all called me in tears,” he said. “I couldn’t bear hearing the words. You have to borrow a lot of money for this journey, and now you had hoped your daughter, your son can be successful, and that you can have some money to pay the debt. Now, it’s hopeless – nothing.”

He went on, “Nothing is OK, as long as they are arrested or in prison. It’s OK, they survived. But now they lost two things. They lost hope and they lost their lives. Nothing.”