The Westminster site was first used for Anglican church meetings and administration in 1888. In 1891 - 1902 a new design for the whole site was partially built but never completed.
The current building is Listed. From the Listing text: Assembly Hall, chapel and offices. Built 1936-40 by Sir Herbert Baker and A.T. Scott for Church of England.
Facades on: Dean's Yard, Great Smith Street, Little Smith Street and Tufton Street. Used by Parliament and the United Nations during and after WW2.
The photo shows the assembly hall.