Q-Whitehall is the (possibly unofficial) name given to a communications facility under Whitehall.
The facility was built in a 12 ft (3.7 m) diameter tunnel during World War II, and extends under Whitehall from Trafalgar Square to King Charles Street. The project was known as Post Office scheme 2845. A detailed description, with photographs, was published just after the war in the January 1946 edition of the Post Office Electrical Engineers Journal.
Sites equipped with unusual amounts of GPO/BT telecommunications plant are given a BT site engineering code. This sites code was QWHI, and this is presumably the origin of the name Q-Whitehall.
The site provided protected accommodation for the lines and terminal equipment serving the most important government departments, civil and military, to ensure the command and control of the war could continue despite heavy bombing of London.
At the northern end, the tunnel connects to a shaft up to the Trafalgar Square tube station, and to the BT deep level cable tunnels which were built under much of London during the Cold War. At the southern end, an 8 ft (2.4 m) diameter extension (Scheme 2845A) connects to a shaft under Court 6 of the Treasury Building: this provided the protected route from the Cabinet War Room. The 8 ft tunnel was further extended (Scheme 2845B) to the Marsham Street Rotundas.
Access to the tunnel is gained via an 8 ft (2.4 m) lateral tunnel and a lift shaft in the nearby Whitehall telephone exchange in Craigs Court.
Spur tunnels, 5 ft (1.5 m) in diameter, were built to provide protected cable routes to the major service buildings either side of Whitehall.
The Whitehall tunnels appear to have been extended in the early 1950s. Some official documents refer to a Scheme 3245: this is the only numbered tunnel scheme that has never been officially revealed or located by researchers