Don't we need migrants to help pay for our pensions?
This is false. Immigrants themselves grow older so the only effect, even of very large scale immigration, is to postpone by a few years the impact of an ageing population. The real answer is that, as people now live longer, they should work longer. The Turner Commission on pensions dismissed the argument that immigration would help with pensions saying that only high immigration can produce more than a trivial reduction in the projected dependency ratio over the next 50 years...and this would be only a temporary affect unless still higher levels of immigration continued in later years... This view was endorsed by the House of Lords Select Committee on Economic Affairs in their report published in April 2008.

http://www.migrationwatchuk.org/faq