Since the immigrants who are already here don't seem to be able to have less than 6-8 children each, some have less but many of them have a lot more, there will be plenty of younger people around to pay pensions, etc. That is presuming that they will be able to find jobs.
Therefore, why do we still need so much immigration? I for one do not want to see this country become an Islamic State, but that's the way we're going.
Imagine it - no more pigs, no more dogs and all rights will be taken away from women. When your grand-daughter is choosing which veil to go out in, will you still want more immigrants?