The farm model is farmers pay minimum wage, and then charge for accommodation. So the actual cost of workers for them is lower than minimum wage.
Similarly, i know of companies that dont advertise work in the UK, its all done thought agencies who advertise abroad and provide accommodation.
I dont think the middle classes realise how many jobs are not only minimum wage, but have difficult conditions. For example, its easy to dismiss workers as not willing to work unsociable hours, but it can be impossible or unsafe to travel for 5am or after midnight using public transport.
I dont blame the companies, they are working in a very difficult market were profits are tight, but i think depending on what is effectively an underclass of foreign workers cannot be a solution.