Probably relating the the sentence directly after the word but, where he says exploiting workers from abroad because they'll accept lower wages and worse conditions isn't the right way to do things.
Maybe it's in the source but I didn't see any of those points in the bit quoted.
I get the desire to give him the benefit of the doubt, but if you take him on his words it's skirting near some pretty ugly stuff. It's a mark of how Brexit has moved the Overton window in UK politics.
Again - why are those sentences together and what is the word “but” meant to mean?