Roughly the same percentage as Germany, France and Iceland.
Why are the other countries much less worried about (legal) migration?
I think it comes mostly down to housing. The UK build ~400 thousand houses in 1971, but last year built 'just' ~140 thousand [2]. There is a huge shortage of housing, and the migrants are blamed for this.
[1] - http://ec.europa.eu/eurostat/statistics-explained/images/7/7...
[2] - http://imgur.com/OEP7Sm2