There is no doubt that immigration has been, and will be continue to be, necessary and beneficial for UK and other countries.
Ahh you forgot to say "selective immigration" would be beneficial. There's a big difference between migrants who have no skills to offer the UK (and are allowed here legally because they are European), and say doctors / nurses/ engineers etc. Those with nothing to offer this country would be best stopped at the border and turned straight around to whence they came from.