4 Cowley Street

4 Cowley Street is a Grade II listed house located in Westminster, London, originally built between 1904 and 1905 by architect Horace Field. Notable for its lavish late 17th-century style and fine Arts and Crafts detailing, the building served as the headquarters for the Social Democratic Party in the 1980s and later the Liberal Democrats until 2011. It has since been restored and converted into a luxurious single-family residence known as Mansion House, currently on the market for £36 million.