Dollis Hill GPO Research Station 1914-1975

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In 1914, the Post Office (who were also involved with telecommunications at that time) set up a research branch of their Engineering Department on a ridge at Dollis Hill in northwest London. At that point, it would’ve been pleasantly rural, and by 1921, a collection of sheds and workshops could be found scattered around the site.
More permanent buildings were erected and in 1933 the majestic main building (built to designs by the Department Of Works) was opened by the prime minister J. Ramsay MacDonald.
Fast forwarding to 2003, the majestic building is still there, although it offers little to an urban explorer interested in derelict sites. After selling the site in the 1980s, the buildings were snapped up by a developer and the main building is now a block of rather exclusive flats


(where my father worked in the 1930s)






I have moved other photographs to a separate page to save time loading this one: click here




In 1933 the GPO Research Station was built at Dollis Hill. In the
late 1930s the Government, anticipating that central London
would be totally devastated by air bombing within weeks of the
outbreak of a European war, built an underground citadel for the
War Cabinet in the Station's grounds. It was hardly ever used.
The GPO Research Station played a much more significant
wartime role than the citadel - the components of 'Colossus',
arguably the world's first electronic computer, were made there
before being sent to the codebreaking centre at Bletchley Park,
Buckinghamshire. The Research Station closed at the end of the
1970s and the site was developed for light industry and, later,
good quality housing.(source)




Following closure of Post Office Research Station, in the mid 1990's the site was sold to a property developer who converted the Research Station into luxury flats with a new housing estate on the rest of the site. The single storey surface building above Paddock was demolished but the citadel, which has local authority listing was untouched and two access points were retained one an unobtrusive steel door in a wall between two houses and the other a brick blockhouse beside the road which also houses a small electricity sub station. The site has now been handed over to a housing association. (source)


Code Breaking at Dollis Hill

Thomas Harold Flowers was born in London on 22 December 1905. He seems to have been a practical child, when told of the arrival of a baby sister he declared a preference for a 'Meccano2' set. After school, he embarked on a four-year apprenticeship in Mechanical Engineering at the Woolwich Arsenal and went to night classes to study successfully for a degree in Engineering from London University.

After graduating, he joined the General Post Office (GPO), which was then responsible for all telecommunications within the UK. He worked at Dollis Hill, the GPO's research station, on experimental electronic solutions for long-distance telephone systems. In the 1930s, that meant thermionic valves (US - tubes), which were seen more as analogue amplifiers than electronic switches. These would replace or enhance the electro-mechanical switches then used. These experiments formed the basis for modern direct dialling, but that was some way off.  (source)


As early as 1920, the electronic valve had been shown to perform switching in a millionth of a second. This notion provided the springboard that was needed. Surely, it was time to embark on a new project and so it was called the 'Heath-Robinson' project. This project was unique and cutting edge at the time. It would yield a one of a kind machine using a tape reader to send pulses of light to a collection of photoelectric cells. Of course, in doing anything new there were inevitable problems. The electronic valves were not reliable and gave off a lot of heat thus experimental machines would have a tendency to smoke. Another problem was that because of the speed required, the tape used would tear on occasion.

Improvements were made to the design. One of the most notable was from Tommy Flowers, an engineer, who suggested to have internal data storage. This however, required over 1,500 electronic valves - which is how the name Colossus came about. As sceptical as this operation was, the engineers at Dollis Hill, a manufacturing plant, went ahead and built Colossus I. Even though multiple engineers contributed to this development only a few esoteric individuals knew about all of its parts and its exact purpose. Alan Turing was actually one of the chief consultants for this project. After working intensely in Hut 8 against the German U-boat fleet and after a visit to the U.S., Turing aided Max Newman greatly from a scientific sense but did not directly work on Colossus. Nevertheless, beginning in February 1943, the Colossus was finally built and installed at BP by December of the same year. The reliability factor increased when the machine was left on continuously. Thus, Fish encrypted messages were being broken at an average rate of 300 per month.(source)

The mathematician Max Newman conceived a way to automate the effort to crack Lorenz codes, one reason why the document on the Colossus, The Tunny Report, is often dubbed "The History of the Newmanry". The result - the room-sized Colossus I - was born in 1943, the descendant of a prototype called the "Heath Robinson". Containing 1,500 valves, 10 times more than electronic machines of the day, Colossus I was built at the Post Office Research Station at Dollis Hill by Dr Tommy Flowers and colleagues (source).

Full technical details and history of Colossus can be found here.

The Colossus was first built in the AC BRIDGE LABORATORIES on the ground floor at Dollis Hill.

(according to Brian Johnson in 'The Secret War')


The artistic talents of John Gibbons, Professor of Sculpture at Winchester School of Art, University of Southampton, have been called upon to commemorate the regeneration of a site of great scientific significance. His sculpture 'Enigma' has recently been unveiled on the site of the old Post Office Research Centre, birthplace of 'Colossus', the first working computer which British scientists developed to break the Enigma code used by Nazi U-boats in World War II.

The 'Colossus' machine was refined at the British wartime cryptanalytic headquarters, Bletchley Park, where mathematical genius Alan Turing used the new electronic technology to detect weaknesses in the U-boat encryption system, resulting in the Allies regaining the battle in the Atlantic, and ultimately the war itself.

The original listed building, site of John Gibbon's 'Enigma', stands on Brook Road, Dollis Hill, London, which is also the site of one of Sir Winston Churchill's secret bunkers during the Blitz. The vast bunker provided a safe place for the Cabinet to meet during air raids.

The site of the old Post Office research Centre has been carefully redeveloped by Network Housing Association, Countryside in Partnership and Copthorn Homes to create new houses and apartments for the Brent community.

Professor Gibbon's sculpture marks the culmination of a two-year development project. 'Engima' was unveiled by the Mayor of Brent, councillor John Lebor, as a striking tribute to the site's place in the history of war-time London and of ground-breaking innovation. (source)


Dollis Hill's underground secret: Dollis Hill - Standby WW2 Cabinet War Room (Paddock)

Paddock was built at the start of the 2nd World War below the Post Office Research Station in Dollis Hill. The purpose of the two level citadel was to act as a standby to the Cabinet War Rooms in Whitehall. The bunker became operational in 1940 with the War Cabinet meeting there on 3rd October.

Churchill did not like the new bunker and by the autumn of 1943 the standby cabinet war rooms were relocated to the North Rotunda in Marsham Street, close to Whitehall; Paddock was abandoned the following year. (source)


n the late 1930s the Government, anticipating the bombing of London at the outbreak of the war, built and underground bunker for the War Cabinet in the GOP's Research Station grounds. Despite fully equipped and staffed throughout the war, it was hardly used and fell into disrepair (source).


Other Uses?

Dollis Hill the rather ugly Victorian building in North London where the Post Office had its research HQ in the 50's. John Taylor ran his mail experimental laboratory for MI5 and MI6 in the basement behind a door marked "Post Office Special Investigations Unit Research".  (source)

The first British clock
The Speaking Clock service was inaugurated in London on 24th July 1936 with a pair of clocks in Holborn exchange (they had been developed by the Post Office Research Station at Dollis Hill, north London). A second pair of clocks was installed in Liverpool during 1942 as a safeguard against interruption, with a 'ring main' connecting both sets of clocks by diverse routes to all exchange centres in the country. (source)

BT's summary of technical advances involving Dollis Hill click here



pdf of Robert Eric Swift's chronology

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last updated: 02 Mar 2005

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