MoD CORSHAM: Prime Minister's Rooms and Operations Rooms


Heritage Category:
Scheduled Monument
List Entry Number:
Date first listed:
Location Description:
Prime Minister's and Operations Rooms, SQ7, Below Ground at MoD Corsham, Wiltshire


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The building or site itself may lie within the boundary of more than one authority.

Location Description:
Prime Minister's and Operations Rooms, SQ7, Below Ground at MoD Corsham, Wiltshire
Wiltshire (Unitary Authority)
National Grid Reference:


A group of rooms built from breezeblock and brick into the existing stone pillars of the former Spring Quarry. This group of rooms would have been central to the operation of the Central Government War Headquarters (CGWHQ) in the event of occupation, providing living accommodation for the Prime Minister, a map viewing room and an observation or briefing room.

Reasons for Designation

The Prime Minister’s and Operations Rooms in CGWHQ, below MoD Corsham, are designated as a Scheduled Monument for the following principal reasons: * Period: the peril from the threat of nuclear strike that Britain faced during the Cold War is inherent in the need for an operational hub and centrally located accommodation for the Prime Minister following a nuclear strike; * Rarity: the site itself is unique, and this set of rooms would have been at the heart of operations in the event of nuclear strike; * Documentation: the CGWHQ telephone system directory provides evidence of the intended use of the set of rooms; * Survival: the rooms retain their communications infrastructure, and map pin boards remain on the walls; * Group Value: the CGWHQ site is an unparalleled example of our national Cold War defence heritage, and represents the systematic use of expansive underground areas by industry and the military during the C20. * Representative: the sober fitting out of the Bath Stone chamber, with breeze block partitions is redolent of the grim character of the Cold War era and the functional nature of the area.


The Corsham Mines are a multi-layered historic site near Bath, beneath the southern end of the Cotswold Hills in Wiltshire. Quarrying of Bath Stone in the wider area took place from Roman times, and by the C18 Bath Stone had become a highly sought after building material. The opening of the Kennet and Avon canal in 1810, and the subsequent construction of the Great Western Railway in the 1840s, made the transportation of the stone to farther locations easier and cheaper, thereby increasing its popularity. Brunel's cutting of the Box Railway Tunnel, beside the village of Corsham, revealed a rich seam of high quality stone beneath the hills. Intense quarrying followed, leaving a network of quarries with worked-out chambers and air shafts, including Spring Quarry. By the time mining ceased in 1940, there were over 60 miles of tunnels across 3,000 acres, located at depths between 80 and 100 feet below ground.

The Bristol Aeroplane Company (BAC) at Filton, near Bristol was bombed in September 1940. In response, Lord Beaverbrook, of the Ministry of Aircraft Production (MAP), issued an urgent plan to relocate all production below ground, which was endorsed by Churchill. The limitations of time, suitable sites, and wartime resources quickly saw the scheme scaled back to the relocation of Filton's engine plant. In December 1940 four quarries were requisitioned by the Ministry, including Spring Quarry, to the south of the Box Tunnel. It covers a vast 3,300,000 square foot area (or 76 acres). It was intended that BAC would convert Spring Quarry for engine production in 6 months, at an estimated cost of £100,000.

However, the scale of the Ministry's factory construction project was enormous, involving the removal of thousands of tons of rubble stone, the levelling of floors, and the strengthening of pillars and roofs using steel and concrete. Lifts, escalators, and an extensive ventilation system were installed. Furthermore, BAC became doubtful about the practicality of the project, and their involvement was scaled back. The factory was not ready for use by the end of 1942, when German bombing had largely ceased, and the need for the underground factory programme had all but vanished. The MAP factory was reclassified as a shadow factory, and proposed production was switched from the Hercules engine to the less vital Centaurus. By 1945, the factory still fell short of its original specifications, and its cost had risen to many millions. Throughout the war, engine production figures were negligible and the factory closed at the end of the war. MAP itself was abolished in 1946. Spring Quarry was bought by the government in 1954, when the north-east area was allocated for conversion to a secret CGWHQ for use in the event of nuclear conflict.

The first known planning for the dispersed operation of government departments, should Central London be destroyed through enemy attack, was during a sub- committee of the Committee of Imperial Defence under Sir Warren Fisher in 1937. Following the war, it was acknowledged that developments in weapons meant that the government's emergency plans were inadequate. In the light of the huge sums spent developing the MAP factory in Spring Quarry, estimated at £30 million, the Treasury proposed buying the requisitioned quarry for use as a citadel for future emergencies. However, the quarry was not bought from the Bath & Portland Stone Company until April 1954, along with 100 acres of land above ground. In 1957 the plans for the emergency headquarters were finalized; the site was intended to provide a safe haven from which the work of Government could continue. From here, the reconstruction of the country following a nuclear attack would be overseen. It was designed to accommodate up to 4,000 military and government staff, including the Prime Minister and key cabinet officials. Occupants would be sealed underground for 30 days and co-ordinate with Regional Seats of Government around the country, meaning that extensive communications and welfare infrastructure was needed.

Work began in 1957 with the construction of a reinforced concrete wall separating the CGWHQ area from that part of Spring Quarry used by the Admiralty. A buffer zone between the two was lined by a concrete block partition and solid rock pillars, sealing the Central Government side. Three blast doors were installed. New ventilation shafts were created and reinforced. Internal areas were divided by concrete block or, in some cases, with red brick. The northern parts of the main roadway through Spring Quarry (now called East/ West Main Road) were converted to a large telephone exchange, stores and plant rooms. Those to the south were offices and accommodation for the Government departments and War Cabinet, a communication centre, and an extensive canteen and kitchen facility. Most of the major building works were complete by April 1959.

The CGWHQ complex was never needed or used for its intended function, and was reduced in capacity over a number of phases during the late C20. The site was de-commissioned in the early 1990s. It was de-classified in 2004.


PRINCIPAL ELEMENTS: a group of rooms built from concrete block and brick into the existing stone pillars of the former Spring Quarry. This group of rooms would have been central to the operation of the Central Government War Headquarters in the event of occupation, providing living accommodation for the Prime Minister, a map viewing room and an observation, or control room.

DESCRIPTION: the Prime Minister’s Rooms comprise two adjacent rooms numbered 34 and 35. They are roughly 6m square in plan, orientated north-west to south-east. Room 35, to the north, is the inner chamber, reached only through room 34. It is built partially into the quarried rock face, and partially in concrete block, with brick supporting columns. The walls are built to approximately 2.5m in height, above which they are divided by wire mesh. Room 34 has access doors from the corridor and from room 36, to the west. The rooms are fitted with an internal telephone and bell system.

Across a corridor to the south of the Prime Ministers rooms are the map viewing room and operations room. They comprise an observation, or control room to the north, numbered 45, overlooking the large map viewing room, numbered 44, and two small storerooms adjoining this to the south, numbered 44A and 44B.

Access to the observation or briefing room is within a few metres of the Prime Minister’s rooms, up a short flight of concrete steps. It is roughly 7m square, built of concrete block and has a large, timber-framed horizontal window running the length of its south-east wall, giving a view down on to the map room. The map room is a roughly rectangular room, 17 x 8m, orientated south-west to north-east; it is built partially into the quarried rock face and partially in concrete block. The wall separating the map from the control room is built from red brick, and there is a painted brick column in the map room. Access is via a doorway from the corridor to the north-west, from the south through room 44B, and via the third store room, numbered 51, not included within the area under assessment.

There are three 1.5m² pin boards fixed to the east, south and west walls, intended to hold maps and be visible from the briefing room.

The doors to all the rooms are timber with plain round door handles, with painted numbers on the outward sides.

The two small storerooms are breeze block between stone pillars. Room 44B provides access between the map room and East Second Avenue to the south. A bathroom with porcelain fittings is located nearby, and denotes the high status of the area. It includes a toilet, urinal, sink and drinking fountain.

All above ground structures are excluded from the scheduling. The designated area includes a 1m margin on all sides as well as above and below.


Books and journals
Catford, N, Burlington, (2012)
Hennessy, P, The Secret State, (2010)
McCamley, N J, Second World War Secret Bunkers, (2010)
McCamley, N J, Secret Underground Cities, (2000)
McCamley, N J, Cold War Secret Nuclear Bunkers, (2002)
Fox, S, 'Subterranea' in Top Secret - Acid, (2010)


This monument is scheduled under the Ancient Monuments and Archaeological Areas Act 1979 as amended as it appears to the Secretary of State to be of national importance. This entry is a copy, the original is held by the Department for Digital, Culture, Media and Sport.

End of official listing

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