But migrants’ hope that they will earn more money in Britain than in other Western European countries are often illusionary, Mr. Sigona added, leading many to take more unnecessary risks.

“There is this idea that Britain is a better place for migrants than, say, France,” he noted. “Once they’re here, they realize it might not be so true. Yet those back home in Vietnam keep thinking that one more step to Britain will be worth it.”

Ten of the truck victims identified this week were from Ha Tinh, one of Vietnam’s poorest provinces, where officials estimate 41,000 people left in the first eight months of this year. But most of those found in the trailer, 20, were from Nghe An, another impoverished province of Vietnam, according to the Essex Police.

Among them was Nguyen Dinh Tu, a 26-year-old father of two who had borrowed $17,000 to build a house for his family, his relatives said. Mr. Nguyen had worked at a food company in Romania, and later at a restaurant in Germany, before embarking on a final journey to England.

“If you want your life in the village to change,” Mr. Nguyen’s brother said in October, “the only way is to go overseas.”

Last month, a journalist from The Times met several families that feared their relatives were among the victims.

Nguyen Dinh Luong, a 20-year-old farmer whose body was also found in the trailer in Essex, had traveled to Russia and then Ukraine before reaching France in July 2018.