There is a new underclass to the British workplace. No-one knows how big it is.
But, during a three month investigation for BBC News, we found evidence of a new form of trafficking from eastern Europe and within Britain; evidence migrant workers were lured here by deception.
We have uncovered conditions that - taken together - amount to a form of bonded labour which is creeping back into the low paid and hidden corners of the country's otherwise booming economy.
Audrius Lelkaitis, a 33-year-old television journalist from Lithuania, agreed to pose for us as a migrant worker seeking employment in Britain. For a month he lived undercover, filming much of what he saw and heard with a secret camera.
Money to a middleman
His story begins in his home country. He went to an agency called ITC. They charged him £180 - the equivalent of about three weeks' wages. In return they told him there was a full-time job waiting for him in Hull.
He would work between 35 and 50 hours a week in a factory and be paid the national minimum wage of £5.35 an hour.
They sent him to a middleman who met him Paddington station. He was asked to pay a further £160.
The agent refused to issue a receipt and it turned out the company he represented had no licence to operate and had even been dissolved as a company.
The Paddington middleman - a Russian-speaking Latvian called Alvis - showed Audrius how to get to Victoria coach station to take a bus to Hull and then disappeared with the cash.
This is how the debt into which migrant workers are trapped deepens.
When Audrius got to Hull he contacted Focus Staff Ltd on the number he had been given. They said they had never heard of him - despite all the money he had spent.
There was no job waiting for him in Hull after all. Focus gave him a bed in a shared room and told him to wait.
He waited six days. Then he was told he was being moved to another part of the country - he had 20 minutes to be ready.
Moving people around the country without their consent is a form of trafficking. Yet Audrius, in debt and with no work, had no choice.
"UK legislation says that trafficking occurs when violence, intimidation or deception is used in to bring a migrant worker to the country and deception was clearly used in this case," Mike Kaye of the independent pressure group Anti-Slavery International told us.
Focus took Audrius to North Yorkshire and gave him a bed in a converted farm building near Richmond.
There were more than 20 migrant workers already living there. There were 12 people in his room alone - men as well as women, including one couple.
They shared one shower and two toilets. There was no privacy. Focus Staff Ltd deducted up to £50 a week from the wages of each employee for rent.
Audrius was given work first in a chicken hatchery (one shift only), then in a chemical packing plant. He did night shifts.
He received his first wage packet at the end of his third week. He had worked 128 hours. The pay packet had £47 in it. The pay slip showed he had been paid only for 20 hours.
His fellow workers told him this was because Focus Staff Ltd withhold wages for two weeks and pay two weeks in arrears.
The payslip also showed he had been paid at an hourly rate of £4.85 - 50p less than the legal minimum.
Mr Lelkaitis had money deducted without warning
There was a further discrepancy. The payslip recorded that he had been paid £97 - not the £47 cash it actually contained. There was no record that £50 had been deducted for rent.
Audrius now had £47 in his pocket; he owed £40 to fellow workers whom he had borrowed from to buy food during the previous three weeks.
We took Audrius's case to the government body that regulates the employment of migrant workers.
Mike Wilson of the Gangmasters Licensing Authority said: "It is clearly in non-compliance with our standards and, I would suggest with the law of the land as well."
Many we spoke to said it was common for them to go a week, or a week-and-a-half, without work. Often, they would work only one or two days a week.
They still have to eat, and pay rent. The more that happens, the harder it is for a migrant worker to reduce his debt; and the deeper the debt, the greater the dependence on the good will of the gang master.
Bonded by debt
Hundreds of thousands of migrants have come to Britain since the enlargement of the European Union in 2004. Many are prospering. They are net contributors to the Exchequer.
But those at the bottom of the heap - the unskilled, who do not speak English - are becoming a new kind of workforce.
They come expecting a reasonable and appropriate wage and in the belief that they will work full time.
And they find themselves part of a vast and shifting pool of casual day labourers, not knowing each day whether they will be working tomorrow or not, and often bonded to their employer by debt and circumstance.
Was that what open borders and flexible labour markets were intended to create?