Thames House, London

Constructed between 1929 and 1930 by John Mowlem & Co., Thames House initially served as offices for Imperial Chemical Industries (ICI). Designed by Sir Frank Baines, Thames House features a style that aligns with the 'Imperial Neoclassical' tradition of Sir Edwin Lutyens and complements the design of Lambeth Bridge, which was also being redesigned during that period. The building’s facade is adorned with statues of St George and Britannia, sculpted by Charles Sargeant Jagger.

Originally, between 1934 and 1939, Thames House was partially used by MI5, occupying the top floor of the South Block. In the late 1980s, as MI6 sought new headquarters, Thames House became available and was chosen for MI5. The GMW Partnership was tasked with redesigning and refitting the building for MI5’s needs, while Mowlem undertook the reconstruction work starting in 1990. This transformation included partially infilling the building's distinctive archway and installing an automated miniature monorail system to transport files from the basement to staff offices.

The refurbished Thames House was officially inaugurated on 30 November 1994 by Prime Minister John Major, marking its new role as the headquarters of the United Kingdom's internal Security Service (MI5). On 1 June 2007, the building, excluding its access steps, was designated as a protected site under Section 128 of the Serious Organised Crime and Police Act 2005. This designation made unauthorized entry into the building a specific criminal offense, reflecting its critical importance to national security.

Today, Thames House stands not only as a monument to early 20th-century architectural design but also as a vital nerve center for the UK's internal security operations.