Do employers take advantage of undocumented migrants?

Of course - you are not going to get premium rates without documentation. It's difficult enough for any emigrant to get a similar employment status than he or she had in their home country unless they pocess a qualifacation recognised and certified in the country that the migrant is arriving in.

Commerce is commerce, capitalism is capitalism. Whether the emigrant's lot improves in the short term can depend on their atttitude towards the work too..many may just see is as temporary work used to pay for some food and accomadation - a stepping stone onto something else.

However there are provisions in the UK to prevent some of these abuses taking place...there is both a national minimum wage which is legally binding on the employer and a recommended London Living Wage