A mosque frequented by the leader of the airline plot terrorist cell has been a recruiting ground for extremists for more than 20 years. The Queen’s Road mosque in Walthamstow, northeast London, where Abdulla Ahmed Ali met his associates, is controlled by the ultraorthodox Tablighi Jamaat. Intelligence services around the world believe that Tablighi’s fundamentalism makes some of its followers easy prey for terrorist recruiters. Two decades ago the same mosque was hosting talks by followers of Omar Bakri Mohammed, one of the first Islamic clerics in Britain to preach jihad. The disclosure of the mosque’s history indicates that, despite...