sentences:  The current incumbent is Ata'ul Mujeeb Rashid who has served as Imam since 1983.In 1984 the Government of Pakistan promulgated Ordinance XX which prohibited Ahmadis from any public expression of the Islamic faith, rendering the caliph unable to perform his duties as the leader of the Community.In response Mirza Tahir Ahmad, the fourth caliph, left Pakistan and migrated to London, provisionally moving the Ahmadiyya headquarters from Rabwah, Pakistan to the Fazl Mosque in London.