It is naive to imagine that post brexit, employers will stop treating low paid workers shoddily - moving them around to line their pockets etc. It's all smoke and mirrors. To take just one example, May's much trumpeted plan to restrict executive pay to a multiple of the average wage. If this becomes law, organisations with a large number of low paid workers eg retail, hospitality, etc will simply transfer the employment contracts of the lowest paid workers into a different legal entity - maybe even outsourcing them to a third party - initial, serco, Mitie etc so that they can pay their executives whatever they want, as they no longer share the same employer. And hey presto all these workers will actually be more insecure and worse off, not better.
It is always the same. The structural inequality in our labour market has nothing to do with importing 'cheap migrant labour'. Rather it has to do with determined government efforts via eg anti trade union laws, employment tribunal fees etc etc to crap on workers and facilitate insecure ('flexible') employment arrangements ever since 1979. In this, they have been aided by a right wing press that has persuaded people to 'blame the immigrant'. It's too late now, and no amount of 'citizens of nowhere', 'hardworking families' etc bollocks can change it. At least we are now a nation of entrepreneurs, looking on the bright side.