Most, if not all, the Poles etc. who work in UK have their passports taken from them by the gangmasters. They are charged for their meagre and sometimes condemned accomodation, charged for transport to and from the fields they work in and have 'deductions' made to pay for NI, health insurance etc. Often, these charges are far greater than they need to be, the extra going in the pockets of the gangmasters. They have no contract that would be any use in a court.
This has been going on for years, since the 50s and is only now beginning to be stamped out, but it will take years.
Freedom to choose is not an option when you have no money, no passport and no hope of any realistic help from the authorities.
The UK is probably the worst of all in the EU for this practice.