Heritage Category:
Listed Building
List Entry Number:
Date first listed:
Statutory Address:


Ordnance survey map of BLOCK B, BLETCHLEY PARK
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Statutory Address:

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

Milton Keynes (Unitary Authority)
West Bletchley
National Grid Reference:
SP 86581 33967


721/0/10010 Block B, Bletchley Park 19-NOV-04

GV II Block B. 1942 by HM Office of Works, adapted in consultation with GCCS from a MOW Temporary Office Design. MATERIALS: steel frame with pre-cast concrete floors and roofs. Painted Fletton brick walls, metal windows. PLAN: attached to Block A to west. Dog-leg plan, with spurs to south, east of the main entrance, and to the north. EXTERIOR: two storeys and basement, with higher entrance block at west end; tall boiler house chimney within east range. Entrance with fluted pilasters and upswept canopy. Plain brick exteriors with regular fenestration, mainly consisting of rectangular 12-pane metal casement windows; those along the south end of the southern spur have been altered through the later insertion of taller openings. Concrete bands at first floor and roof levels. Later single storey timber-clad extension to north of no interest. INTERIOR: Considerably altered. The entrance lobby has been enlarged, through the demolition of some war time rooms (in the 1950s) and leads to an open staircase with tubular steel railings. Smaller staircase at north end of east range. Each floor formerly consisted of a spine corridor with offices on each side (or WCs along the north side of the main range). The centre and western parts of the ground and first floors have been opened out to create display areas, although the size and location of the wartime offices is still sensed through the exposed steel and concrete beams, under which the original plasterboard partitions were positioned. Some individual rooms remain at the east end of the building, but many of these date from the 1950 conversion to study bedroom use, which used clay brick construction for the walls (some of the clay blocks walls date from the war time construction). The arrangements of war time structures, especially with regard to pantry and store facilities can still be discerned in the areas of the building which have not seen recent change, through changes in fenestration and identification of war time and later materials that still survive. HISTORY: The HQ of the Foreign Office's Government Code & Cypher School was established at Bletchley Park in 1939. It has become celebrated for its contribution to Allied victory in the Second World War, and is also renowned for its contribution to the development of information technology. Block B, was conceived in mid-1941 as an extension to the overcrowded huts, and completed in late Summer 1942. They formed the first wave of purpose-built structures on the site, which responded to the increased volume of decrypts and the desire to create an effective military intelligence centre. It originally housed the Naval and Air Sections. The ground floor was used by the Registry for the western European Cryptography Section: other parts were used by the Japanese Cryptography Section. From later in 1943 the naval Section took over the block. After the war the building was first used as a National Service Hostel: in mid 1950 various alterations took place to convert the block into accommodation for the teacher training college which had been established in 1947. Subsequent modifications took place in the late 1970s when the Civil Aviation Authority took over the block. Empty since 1993, the block has recently (2004) been adapted for use as a museum. SUMMARY OF IMPORTANCE: Block B's importance is principally historical, although the physical survival of the building which reflects the scale of the operation at Bletchley is important. Block B demonstrates the first approach of building more permanent buildings on the site using a bespoke design after careful planning. It has a significant relationship to the lake and landscape as well as the other war time buildings that still survive. Bletchley Park is renowned for its part in breaking the German Enigma code, and in contributing to Allied victory (especially in the Battle of the Atlantic). Block B played an important role in this achievement. The building is one of a number of structures at Bletchley Park which clearly reflects the development of the complex. Architecturally the building possesses some outward interest as an increasingly rare example of a rapidly constructed wartime office building, and retains its original crisply functional appearance. The interior has been substantially altered and little of the surviving fabric dates from the crucial period of the block's history. SOURCES: Bletchley Park Interim Report, Historic Buildings and Areas Research Department Reports and Papers 2004, Series Number: B/003/2004, English Heritage. pp 48-73. Lake, Jeremy, Bletchley Park Conservation Management Plan (draft), English Heritage 2004. Evans, David, 'BP' The development and historical function of the fabric, April 2003. Enever, Ted, Britain's Best Kept Secret - Ultra's Base at Bletchley Park, Sutton Publishing, 1999. Sebag-Montefiore, Hugh, 'Enigma' The Battle for the Code, Phoenix, 2001


The contents of this record have been generated from a legacy data system.

Legacy System number:
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Books and journals
Enever, T, Britain's Best Kept Secret, (1999)
Evans, D , BP The Development and Historical Function of the Fabric, (2003)
Sebag-Montefiore, H, Enigma The Battle for the Code, (2001)


This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.

End of official listing

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