Western Europe's population, which was nearly four times that of the Middle East plus North Africa in 1950, is now only one-third larger, and will be at parity by 2025. By mid-century, the population of the Middle East and North Africa will be around one-third larger than Europe's population. In the meantime, the Muslim population in Europe will also soar, perhaps to around one-third in the major cities, both because of in-migration and because of higher fertility rates of European Muslims compared with European Christians.

http://www.bbc.co.uk/radio4/reith2007/lecture3.shtml