I am a migrant myself and came to this country 16 years ago. I can understand some of the sentiments people are expressing here.
Basically from my life experience with regards to natives vs immigrants, you get two kinds of people. You will have both immigrants and natives who understand and appreciate each other cultures and wish to learn from each other. Hence the social interaction is facilitated between two groups by forming friendships maybe at schools, colleges, universities and workplaces.
Then you get the opposite kinds who don't want to assimiliate with each other and form barriers between different communities. These kind of people whilst contributing within their own communities won't feel the need to experience life outside their shells. In this case you will have immigrants who perhaps have resided in this country for 20-40 years and yet still can't speak the host country language.
Likewise you will also have natives in this group who have never experienced any ethnic minority cultures in this country and remain ignorant and form negative stereotypes about the latter.
The beauty of being a contributing immigrant in this country is that you can view and taste life from a different perspective and can have many enriching life experiences
As for people who are saying that immigrants still can't speak the host language after residing in this country for so long; their questioning is perfectly justifiable as learning the host language breaks down many barriers.
However I must also put forward the same question to those fellow british ocukers who may have family, friends living and working in the middle east/asia. How much do they know the host language of those countries?