140 Gower Street was the headquarters of the Security Service (MI5) from 1976 to 1994.

In the late 19th century the site at 140 Gower Street was occupied by a modest three-story building which was used by George J. W. Pitman, book publishers.

[6] After the bookshop was demolished, the site was redeveloped and a new ten-story building constructed in the early 1950s.

[7] The new building was occupied by various government offices including the Commission on Industrial Relations.

[8] The Security Service (MI5), who had relocated from Leconfield House, occupied the new building, known simply as "140 Gower Street", in 1976:[9] the Director-General's office was on the 6th floor.