To be privately owned
Lancaster House

Lancaster House is a residence in London, England, that established itself as a social hub.
History+
The construction of Lancaster House began in 1825, commissioned by Frederick Augustus, Duke of York and Albany. Following his death in 1827, the unfinished structure was acquired by the Stafford-Sutherland family. Under their patronage, the estate was completed in 1843 and evolved into one of London's important social gathering places. It received its current name in 1912 from William Lever, 1st Viscount Leverhulme, who named it after his birth county and gifted it to the state in 1913. Until World War II, it housed the Museum of London and today serves as a venue for state receptions and conferences, including the signing of the Lancaster House Agreement in 1979.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.5039, -0.1391