The Briton is facing a possible lengthy prison sentence and huge fine if convicted – but human-rights groups say he is being victimised in an attempt to silence him

British labour-rights activist Andy Hall is facing eight years in prison and a $13m (£8m) fine for defamation after writing a report alleging labour abuses in the Natural Fruit Company, a large Thai pineapple wholesaler that supplies the EU. He wrote that, among other things, the passports of migrant workers were confiscated and there was violence against employees.

It is a case that human rights groups claim is a “complicit cover-up” by the government, an attempt to shoot the messenger rather than improve working conditions, and NGOs, industry experts and hundreds of thousands of people all over the world have signed petitions calling for Natural Fruit to drop its charges against him.

But Hall, whose civil and criminal trial began in Bangkok at the beginning of September, has no choice but to face the courts. His passport has been confiscated and additional charges against him levelled just one day after proceedings started. “They are basically making my life impossible,” says Hall, 34, in what he claims is an effort to silence him. “I have to focus my whole life on defending myself.”

Born in Lincolnshire to working-class parents, Hall was the first child in the family to go to university. After graduating with a first-class honours degree in law from University College London, he worked briefly with criminal offenders in Oxford before taking a PhD in corporate social responsibility in Melbourne and Cardiff, focusing on occupational deaths.

It was a backpacking trip through northern Thailand in 2004 that sparked his interest in migrants’ rights. Meeting Burmese construction workers who had been disabled on the job and left without any medical or financial support, Hall says he felt a strong desire to “both empower migrants to stand up and fight the abuse they were facing” but also “to create a system and policies within the Thai system to allow them to stand up and fight”. Even now, he adds, migrant workers – who comprise as much as 10% of Thailand’s workforce, primarily in the fishing, construction, canning and agriculture sectors – are not allowed to form unions in Thailand, and their rights are still severely limited.

In the 10 years he has worked in Thailand and neighbouring Burma, Hall – who speaks both Thai and Burmese – has made impressive gains steering migrant workers’ groups in the two nations; advising Burma’s intelligence services on migration issues and policies; helping to develop passport systems so that migrant workers can be regularised; and organising personal friend Aung San Suu Kyi’s hugely publicised visit to Thailand in 2012 to meet with thousands of Burmese migrant workers in the fishing and canning industries.

But his high-profile work has not often been met with open arms, particularly in Thailand, where he claims the government has never been willing to tackle trafficking or migration – two serious issues in a nation where up to half a million people are thought to live in slavery. Then there are the worrying phonecalls. Hall says one caller – who claimed to be a relative of Natural Fruit’s owner, Nai Wirat – recently phoned to verbally attack him. And there have been warnings of worse: a Thai deputy minister personally told him that he was putting his life in danger.

Still, Hall is defiant and unapologetic in the face of such adversity. “What I did was in the public interest for the benefit of migrants, and that’s what I’ve been doing for 10 years,” he tells the Guardian, during a break at court. “I’m not going to back down because I’ve done nothing wrong.

“My work is not negative, it’s not bad, it’s not vicious – it’s intended to make things better. If they’re not willing to drop the cases, I am certain they, the pineapple industry, the Thai export industry and the Thai economy will suffer more.”