Many foreigners who come here to work are not "Immigrants" at all.

We don't have a word for it in English, but we need one. The Germans call them "Gastarbeiters" - literally "Guest workers" to describe individuals who come to work in their country - but not permanently to live there. We use the word "immigrant" to cover all non Brits who come to live and work here irrespective as to whether their move here is permanent or not.

A Pole (for example) who comes to the UK to work does so for largely economic reasons. The money is better. Fair enough - EU rules allow this and in the main there is mutual benefit. But unless he formally settles here and in time becomes a British citizen he is not an "immigrant". He has not "migrated" to the UK permanently. He may do so in time of course, but that is not why he came. 

If we could use more accurate language to describe the status of people from abroad who come here to work we might take some heat out of the issue. Sadly the very word "Immigration" has a built-in negative ring about it. The words "Guest Worker" although a bit clumsy are better. The adjective "Guest" is particularly good. We welcome guests and look after them. Let's get our language use right and the rest might follow.