Migrants are shipped in to fill vacancies. No one is losing their job.I'm sure that the Brits who want to work but lose their jobs due to being undercut by foreign workers would rather keep their jobs than be able to buy things for a few pence less.
But the vacancies are often there because the locals can't afford to work for the derisory rates - possibly because they don't want to live 14 to a room and survive on vodka and swan meat.