Of all the errors commonly made by Freepers commenting on this subject, the most persistent is that immigration to the United Kingdom is primarily, or even entirely, Muslim.
Britain also gets lots of African (e.g. Nigerian) and Caribbean immigrants from its former colonies, so even when the immigrants are non-Muslim, they tend to be Third World people who bring poverty and crime with them. Similarly, in the US, most mass immigration is non-Muslim - that doesn't mean that Mexican and Central American street gangs and petty criminals aren't a problem.