Fortress House was a building with its main entrance at 23 Savile Row in London W1, also including 5–9 New Burlington Street.

The building had little ornamentation: rustication on the ground floor disguised a change in levels along Savile Row, and a dental cornice at the top of the central block.

A large entrance porch to central block, with pilasters surmounted by a recessed semi-circular headed niche within an open triangular pediment.

English Heritage was paid £3m to leave in 2006, ten years before the end of its lease, and moved to the old Prudential building at Holborn Bars.

In 2006, the Secretary of State for Culture, Media and Sport issued a certificate of exemption from listing effective until December 2010.