Image copyright Reuters

British labour rights campaigner Andy Hall has left Thailand after a three-and-a-half year legal battle with a pineapple processing company accused, in a report he contributed to, of abusing its workforce.

The dismissal of one set of charges against the British activist was confirmed by Thailand's Supreme Court last week.

However, he was convicted in September on two other counts under sweeping criminal defamation and computer crimes laws and was given a three-year suspended prison sentence. He also faces civil complaints by the pineapple company, Natural Fruit, which is demanding around $12m (£9.6m; €10.9) in damages.

But it was the prospect of further criminal charges over another group of workers he is supporting that persuaded Mr Hall that he should leave Thailand and not return.

He and the 14 migrant workers from Myanmar (Burma) - who have alleged abusive treatment at the hands of a farm which supplied the big Thai poultry processor, Betagro, with chickens - recently had defamation lawsuits filed against them.

Before he left Thailand Mr Hall told the BBC that he felt that the prospect of having to contest continuous lawsuits filed against him would make it impossible for him to defend migrant workers' rights effectively.

Image copyright AP Image caption Mr Hall said continuous threats of legal action had made it impossible to effectively defend migrant workers' rights

The situation for human rights defenders, he said in a statement made as he prepared to depart, has rapidly deteriorated in Thailand, with significantly increased risks.

The challenge confronting Mr Hall is one faced by many Thai activists as well.

Unlike many countries, defamation is a criminal charge that can carry a two-year prison sentence. These days it is commonly used alongside the tougher Computer Crimes Act, which mandates a sentence of up to five years in prison.

Two years ago, the editors of a small newsletter, Phuketwan, were prosecuted by the Thai navy for an article in which they quoted a Reuters news agency report alleging Thai military involvement in human trafficking.

They were finally acquitted last year, but the effort of defending themselves contributed to the newsletter being shut down.

In June this year three prominent human rights defenders were prosecuted under the same two laws by a unit of the Thai military over a report they took part in which alleged the use of torture against military detainees in southern Thailand.

Image copyright Getty Images Image caption Thailand's Prime Minister General Prayuth Chan-ocha seized power in a coup in May 2014

The laws were also invoked by a military officer, who filed charges against the niece of a conscript who was beaten and tortured to death because she had published details of an internal army investigation into his death.

Criminal defamation and computer crimes cases are usually accepted for indictment by the courts in Thailand - lawyers describe the bar for accepting such cases as very low.

Defendants must post bail to avoid immediate imprisonment, and then fight their cases over hearings which can stretch out over many years, with no prospect of recovering their legal costs even if they win. The cases are also usually heard in the location where the plaintiff files the complaint, forcing defendants to travel for each hearing.

Questions have also been raised about some of the verdicts reached by Thai courts. Andy Hall's lawyers believed they would win the cases against him because he was not quoted in the Finnish report and did not write it, but had only contributed background research.

Some human rights groups have described the cases against Mr Hall as "judicial harassment" aimed at inhibiting investigations into labour abuses. They have called repeatedly for the criminal defamation and computer crimes laws to be repealed, arguing that they are a serious impediment to freedom of expression in Thailand.