Twentieth Century Society

The Twentieth Century Society (abbreviated to C20), founded in 1979 as The Thirties Society, is a British charity that campaigns for the preservation of architectural heritage from 1914 onwards. It is formally recognised as one of the National Amenity Societies, and as such is a statutory consultee on alterations to listed buildings within its period of interest.

Source: Wikipedia — Twentieth Century Society (CC BY-SA 4.0)