When Piotr, 60, was promised a job in a meat-processing factory in the UK, he weighed up his options. His wife had recently died, he had just been made redundant, and his daughter – his only remaining relative – lived overseas. He decided the opportunity was worth the risk and agreed to leave his native Poland.

The man who had offered Piotr work also provided two one-way tickets to Britain – one for Piotr, the other for his friend. "We left Poland with a few belongings and €10 [£8] that I borrowed from a friend," Piotr told the Gangmasters Licensing Authority (GLA). "I was worried, but happy that I would be working again."

When the pair arrived in the UK, they were taken to a house where other workers lived. But things did not go according to plan. "My friend and I had to share the double bed – we had no choice," Piotr said. "The room was cold and dirty. Black mould was on the walls, wallpaper was dropping off and the house was damp. My heart stopped."

Piotr knew he could not return to Poland – he had no money, he didn't know where he was, and his English was poor. He was also worried that his daughter would think he was a fool to make such a life-changing, but ill-informed, decision.

Piotr said he regularly worked up to 60 hours a week at the factory. He had to give half of his wages to his bosses and, although he was taken to various banks to open accounts, he never saw the bank cards.

Escape was proving impossible. "I paid my debt [for travel to the UK] after a month, but if I left I knew they would find me and kill me, so I had to stay," Piotr said. "They were always threatening that they would take us to a wood 50km away and we would not leave. I was their property and there was no escape. I lived every day in fear."

Piotr's case is yet another an example of forced labour, which comprises any work an employee is coerced to undertake. "Forced labour is an emerging trend where people are using human beings as exploited commodities," said Paul Broadbent, chief executive of the GLA, which supported Piotr when his fresh start transformed into a nightmare of exploitation.

A report on forced labour in the UK, published this month by the Joseph Rowntree Foundation (JRF), found that the structure of the UK economy, through its light-touch regulation of business and its heavy hand on immigration, has created a low-paid segment of the workforce that is susceptible to forced labour.

"The government isn't really monitoring the workplace in the UK," said Jean Allain, a professor of public international law at Queen's University Belfast and one of the JRF report's authors. "And while there are various agencies in the UK that are meant to monitor the workplace, you find in other countries there are many more."

Allain adds that some foreign nationals – for example, Bulgarians and Romanians – are allowed to enter the UK but are not legally permitted to work, which can push some to seek employment in the informal sector, making them more vulnerable to exploitation.

According to Allain, Piotr's case ticks several boxes: "Are people being threatened so as to work? Yes. Are people in a situation of having to repay a loan? Yes. Does it typically happen to non-UK nationals? Yes – because they are vulnerable, don't speak the language and don't understand the system."

Forced labour is likely to occur where the informal sector – for example, cash in hand – meets the formal economy. "Let's say the profile of an exploiter is someone who is working in the grey economy," he said. "This informal sector is the breeding ground or gateway for forced labour."

Allain's team is adamant that forced labour is not a hidden crime – and combatting it requires an understanding of the business motivation behind forced labour: taking advantage of people to make money and generate profits.

"There are links between the informal economy and the formal economy," Allain said. "We need a better understanding of what the entry points for forced labour are and we need to have better intervention strategies to stop it from happening."

Piotr eventually escaped. After being subjected to a series of beatings, he sought help at the job agency where his bosses had initially taken him to sign his employment contract. The GLA became involved in his case, and he is now living in safety.

To disrupt the business of forced labour in the UK, and to prevent people from being exploited, the JRF report calls for tougher, government-led regulation of businesses and for increased social auditing of labour forces.

"What we say is that brands should be worried about their labour supply chains," Allain said. "They should be asking where the labour comes from that creates their products. It's about taking responsibility and going into those labour supply chains and social auditing."