"While mainstream Judaism in Britain is in decline, as people 'marry out’ and abandon the faith, the Haredi community is expanding at a phenomenal rate.
A report by the Board of Deputies of British Jews in 2008 estimated the size of Britain’s strictly Orthodox community at close to 30,000 people, around 10 per cent of the nation’s Jewish population."

http://www.telegraph.co.uk/news/religion/8326339/Inside-the-private-world-of-Londons-ultra-Orthodox-Jews.html