For Loan Hoang, news of the tragedy in Essex brought memories rushing back of how her own brothers risked their lives to help their family flee Vietnam four decades ago.

In 1978, three of them were among 600 people crammed on to a boat made for 400. With the boat barely floating under the weight of its cargo, they set out to sea uncertain whether the voyage would end in safety or death.

“I’m very sad about that,” she said of the news that several Vietnamese were believed to be among the 39 people found dead in a lorry container in Essex last week. At least one was reportedly hoping to help her family pay off debts. “It’s the same as my brothers: they were willing to give their lives for us.”

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The risks the men ran in the 1970s were very real. In more than a decade of Vietnamese refugees fleeing by boat, tens of thousands, perhaps hundreds of thousands, died at sea, drowned or targeted by pirates.

Hoang’s brothers were among the lucky ones. They were rescued by a passing ship, then given asylum in the UK, where their parents and two unmarried sisters were able to join them a year later.

Hoang had been a teacher in Vietnam, but said she did not regret leaving to become a childminder in the UK. “The main thing here is freedom,” she said, after a lunch of traditional pho noodles and broth in Centre 151, which serves the Vietnamese community in north-east London. “When we came here, we didn’t think we could get a job, but I was willing to do anything.”

Thi Thu Nguyen, 53, said she thought she understood why young people took such terrible risks. “Perhaps they know they might die, but they accept it,” she said. “Here they can find jobs with good pay to help their family back home.”

She had a straightforward journey to join her husband. But she says that moving to the UK was such a transformation – albeit a chilly one – that she remembers not just the date of her arrival, but the hour: 1pm on 26 October, 1995. “I was so cold,” she said with a smile. “But it’s a much ­better life.”

Britain’s Vietnamese community is now tens of thousands strong; the last census in 2001 listed more than 22,000 residents born in Vietnam. But without a category for British-born people of Vietnamese heritage, or a count of recent arrivals, the actual numbers are likely to be at least twice as high.

The first significant wave of arrivals from Vietnam was around 40 years ago, in the wake of the civil war. Many were refugees who had fled by sea and their families.

Vietnam has become much more prosperous after its communist leadership opened up the country to foreign investment and loosened economic controls, on a model similar to the one that drove China’s explosive growth. But it still has some extremely poor areas, and both natural and human-made disasters can push people to looking for work overseas to support their families. Some of the people who died in the lorry may have come from an area where a toxic spill has decimated the vital fishing industry.

Although many leave willingly for the UK, hoping to help their families or build a better life, the nature and cost of the journey – which typically costs between $10,000 (£8,000) and $40,000 – means that the line between ­smuggling and trafficking can become blurred.

On arrival in the UK, many are sent to work in cannabis farms or nail bars, sometimes forced into prostitution, paying off the cost of their transport in a form of debt bondage that can last years.

For now the community is reeling, but it remains to be seen whether the tragedy will deter others from making the journey. “It’s very bad news for our people,” said Pham Guang, a retiree at the pho club who left Vietnam more than four ­decades ago. “There is a lot of discussion about it. Of course, I understand these are poor people who might say they can take risks for a better life … but I don’t know how they can decide to come in the lorry. It’s very dangerous.”