I think the point durruti makes is that (a) firms can get people (migrants and otherwise) to work for less than minimum wage as it is and (b) that they are willing to accept lower terms and conditions as they do so. This has an obvious effect on those people at the bottom of the wage scale that does not need the Daily Mail to point it out.
As I said above, there are two ways of looking at and dealing with this - the way the BNP and (to an extent) Gordon Brown + NL has looked at it with the whole British jobs for British workers thing, and then there is dealing with it on the basis of ensuring that noone at that level, migrant or otherwise, is working for such low pay, and in such insecure and unsafe conditions.
Of course the Government
could have dealt with a large part of these problems before the economy nosedived, either via the proposed EU directive
COD 2002/0149, or via the two
Temporary and Agency Workers (Prevention of Less Favourable Treatment) Bills. Instead they killed the EU proposal, have killed off one of the Bills due to time and show every indication of killing the second one off.