The BBC found that signs that victims of modern slavery were being forced to work at a McDonald’s subsidiary and a factory supplying bread to major supermarkets had been missed for years.

The gang forced 16 victims to work in a fast food restaurant or factory that supplied Asda, Co-op, M&S, Sainsbury’s, Tesco and Waitrose stores.

Well-established signs of slavery, including the deposit of four men’s wages into one bank account, were omitted, while Czech victims were exploited for more than four years.

McDonald’s UK said it had improved systems to detect “potential risks”, while the British Retail Consortium said its members would learn from the case.

Six members of a family-based human trafficking ring from the Czech Republic have been convicted in two criminal trials that were delayed due to the Covid pandemic.

Reporting restrictions prevented much of the case from being covered, but BBC England can now reveal the full scale of the gang’s crimes and the missed opportunities to stop them.

Nine victims were forced to work at a branch of McDonald’s in Caxton, Cambridgeshire. Nine people worked for the pitta bread company with factories in Hoddesdon, Hertfordshire, and Tottenham, north London, which produced products under its own supermarket label. A total of 16 victims died at both plants, two of whom worked at both McDonald’s and the factory.

The victims – all vulnerable, most had experienced homelessness or addiction – earned at least the legal minimum wage, but almost all of their wages were stolen by the gang.

Although they lived on a few pounds a day in cramped accommodation – including a leaking shed and an unheated caravan – police discovered their work involved financing luxury cars, gold jewelry and property in the Czech Republic for the gang.

In several cases victims fled home and were then tracked and smuggled back to the UK.

The abuse ended in October 2019 when victims contacted police in the Czech Republic, who then notified their British counterparts.

But the BBC found, by reviewing legal documents from the gang’s trial and interviewing three victims, that warning signs had gone unnoticed for at least four years.

Undetected red flags include:

• The victims’ earnings were transferred to bank accounts in other people’s names. At McDonald’s, at least four victims’ wages – a total of £215,000 – were paid into one account controlled by the gang

• The victims did not speak English, and job applications were filled out by a gang member who could even participate in job interviews as a translator

• The victims worked extreme hours at McDonald’s – anywhere from 70 to 100 hours a week. One victim worked a 30-hour shift. The UN’s International Labor Organization says excessive overtime is a sign of forced labor

• Many employees had the same registered address. The nine victims worked in a bakery in the same terraced house in Enfield, north London

“I’m really concerned that so many warning signs have been missed and that companies may not have done enough to protect vulnerable workers,” said Dame Sara Thornton, a former independent anti-slavery commissioner who reviewed the BBC’s findings.

Detective Inspector Chris Acourt, who led the Cambridgeshire Police investigation, said “enormous opportunities” had been wasted to detect slavery earlier and alert authorities.

“Ultimately, we could have found ourselves in a situation where we could have ended this exploitation much earlier if we had been informed about it,” he said.

Like many victims, Pavel – who waived his right to anonymity – was homeless in the Czech Republic when the gang approached him in 2016.

He claims he was lured by the false promise of a well-paid job in the UK, where he could then work legally.

However, the reality of what he experienced left lasting scars, he added.

“You can’t undo the damage done to my mental health, it will always live in me.”

His exploiters gave him just a few pounds a day in cash, even though he worked 70 hours a week at a branch of McDonald’s, he said.

According to the police, a gang led by brothers Ernest and Zdenek Drevenak confiscated the passports of all the victims and controlled them through fear and violence.

“We were afraid,” Paul said. “If we ran away and went back home, (Ernest Drevenak) has a lot of friends in our town, half the town is his friends.”

According to Met inspector Melanie Lillywhite, the gang “treated their victims like cattle”, feeding them “just enough to survive”.

She said the victims were kept in “invisible handcuffs”, monitored by closed-circuit television, barred from using phones or the Internet, and unable to speak English.

“They were really cut off from the outside world,” she said.

Although the gang was convicted in court, Pavel believes that McDonald’s also bears some responsibility.

“I feel partially exploited by McDonald’s because they didn’t respond,” he said.

“I thought if I worked at McDonald’s they would be a little more careful about noticing.”

Two former colleagues told the BBC the extreme hours the men worked and the impact it had on them.

Like most McDonald’s, the Caxton location – on the A428 – is franchised, meaning an independent company pays the fast food giant to allow it to run the restaurant.

Although the victims worked there between 2015 and 2019, it was run by two different franchisees. We contacted both, but they did not respond.

McDonald’s UK declined our offer of an interview but made a statement on behalf of the corporation and its franchisees.

It said the current franchisee – Ahmet Mustafa – “only came into contact with the full depth of these horrific, complex and sophisticated crimes” while working with the police and prosecutors.

The company said it cares “deeply” for all employees and promised that, by working with franchisees, it will “play our part alongside government, non-governmental organizations (NGOs) and wider society to help fight the evils of today’s slavery.”

It also said it commissioned an independent review in October 2023 and took steps to improve its ability to “detect and deter potential threats such as: shared bank accounts, excessive working hours and reviewing the use of interpreters during hearings.”

The bakery company – Specialty Flatbread Ltd – ceased operations and went into administration in 2022.

None of the supermarkets detected slavery when the victims worked at the factory between 2012 and 2019.

Dame Sara said she would expect retailers to carry out “fairly thorough due diligence”, adding that they tend to “pay much more attention to own-brand products because their reputation is at stake”.

Sainsbury’s said it stopped using the company as an own-brand supplier in 2016.

The others only stopped some time after police rescued the victims in 2019.

Asda told the BBC it was “disappointed that a historic incident has been found in our supply chain”, adding that it will “review each identified incident and act on the findings”.

It stated that it made three site visits but focused solely on food safety and stopped using the factory in 2020.

Tesco said inspections – supported by information from anti-slavery charity Unseen – “found concerns about working practices” and the company “ceased all orders from the supplier” in 2020.

Waitrose said it withdrew in 2021 after audits raised “concerns about factory standards and working conditions”.

The co-operative said it had carried out a “number of” unannounced inspections, including interviews with staff, but had found no signs of modern slavery, adding that the company was “actively working to address the shocking problem… both in the UK and abroad”.

M&S said it suspended and delisted the company in 2020 after it “became aware of potential breaches of ethical work standards via its Modern Slavery Helpline”.

The British Retail Consortium said workers’ wellbeing was “fundamental” for retailers, which it said respond quickly when concerns arise.

“However, it is important that the retail industry learns from such cases to continually strengthen its due diligence,” it said.

Specialty Flatbreads director Andrew Charalambous did not respond to written requests for comment, but in a telephone interview with the BBC he said he supported the police and prosecutors, adding that the company had been “thoroughly scrutinized by leading law firms” and “everything we did it was legal.”

He added: “From our point of view we didn’t break the law in any way, having said that, yes, maybe you’re right that maybe there were some warning signs or things like that, but that would be for the HR department of the department who were dealing with this on the front lines “

The Modern Slavery Act requires larger companies – including McDonald’s and supermarkets, but not factories – to publish annual reports outlining what action they will take to tackle the problem.

Former Prime Minister Baroness Theresa May, who introduced the law as Home Secretary in 2015, admitted the law did not protect victims in the case and believed it needed to be “strengthened”.

The former prime minister, who now heads the Global Commission on Modern Slavery and Human Trafficking, said the case was “frankly shocking” and showed that “big companies are not looking properly at their supply chains.”

She said the global commission was reviewing what new regulations were needed “to ensure companies take action.”

In response to the case, the government said it would “set out next steps on the issue of modern slavery in due course.”

It said it was “committed to tackling all forms of modern slavery” and “will pursue gangs and employers with every lever at our disposal, while ensuring victims have the support they need.”

Additional reporting by Mary O’Reilly and Maria Jevstafjeva

Details of organizations offering support to victims of modern slavery can be found at: bbc.co.uk/actionline