The Decision to Build
The decision to construct deep shelters beneath several of the deep-level tube stations was made in 1940, following the experience of the first months of the Blitz and the recognition that existing shelter provision was insufficient for the scale and intensity of the German bombing campaign. The government had initially resisted the use of tube stations as shelters — fearing disruption to the essential transport network — but public demand and the evident safety provided by the deep tunnels made the policy impossible to maintain. By the autumn of 1940, tube sheltering had become an established fact of London civil life, and the government was obliged to regularise and extend the provision.
The deep shelter programme, approved in November 1940, aimed to provide a network of dedicated shelter tunnels beneath eight of the deepest stations on the London underground, connected to but separate from the operational tube tunnels. Each shelter was designed as a pair of parallel tunnels, each 400 metres long and 7.3 metres in diameter, running beneath and alongside the existing running tunnels at a slightly deeper level. The completed shelters would accommodate approximately eight thousand people each, sleeping in three-tier bunk beds arranged along both sides of the central walkway in each tunnel.
Belsize Park was selected as one of the eight deep shelter sites, alongside Stockwell, Clapham South, Clapham Common, Clapham North, Camden Town, Goodge Street, and Chancery Lane. The selection reflected both the depth of the stations — all were deep enough to provide genuine protection against bombing — and their geographic distribution across London, ensuring that the shelters would be accessible to populations across the city. The particular depth of Belsize Park station, with its platforms more than fifty metres below the surface, made it one of the most secure of the eight sites.
The Construction
Construction of the Belsize Park deep shelter began in 1942, undertaken by the contractors who had long experience of deep-level tunnelling work for the underground railways. The work was challenging: the tunnels had to be constructed in close proximity to the existing operational tube tunnels without disrupting the vital tube service that Londoners depended on for daily travel to war work. The geology at Belsize Park — the London Clay that had made deep-level tunnelling possible in the late Victorian period — was familiar to the engineers, but the precision required to excavate new tunnels immediately adjacent to existing ones demanded the highest standards of engineering practice.
The tunnels were lined with cast-iron segments bolted together — the standard technique for London clay tunnelling — and fitted with the concrete floor and permanent fixtures required for shelter use. The internal fittings included the three-tier bunk beds, canteen and ablution facilities, medical rooms, a telephone exchange, and the ventilation and heating systems required to maintain liveable conditions for large numbers of people in a confined underground space over extended periods. The engineering of the ventilation system was particularly complex: ensuring adequate fresh air supply and exhaust for several thousand people in tunnels fifty metres below ground required careful calculation and robust mechanical equipment.
Access to the shelter was provided by new shafts sunk from the surface to the shelter tunnels, separate from the existing tube station lifts and staircases. These access shafts were built at points along the length of the shelter tunnels, emerging at the street surface through concrete entry buildings — functional, utilitarian structures quite different in character from Leslie Green's elegant terracotta station buildings above. These wartime entry buildings survive in some cases and can be identified in the streets around Belsize Park station, their slightly incongruous presence amid the Victorian terraces marking the buried reality of the tunnels beneath.
Military Use and Secrets
The Belsize Park deep shelter, like several others in the network, was used for purposes beyond civilian shelter during the war years. The particular depth and security of the tunnels made them attractive for military and government uses that required protection from bombing combined with confidentiality and controlled access. The exact nature of these uses has been the subject of considerable research and speculation, and the records that have entered the public domain reveal a more complex picture than the simple civilian shelter narrative suggests.
It is known that portions of the Belsize Park deep shelter were used for document storage, communications purposes, and possibly for military planning activities during the later war years. The depth of the tunnels provided a degree of protection that no surface building could offer, and the discrete access arrangements of the shelter — quite separate from the public tube station above — made it possible to maintain controlled access without the knowledge of the general public. The wartime culture of official secrecy, which was both necessary and pervasive, has left many aspects of the shelters' military use difficult to establish with certainty.
The neighbouring shelter at Goodge Street was used as a headquarters facility by General Eisenhower during the preparations for the D-Day landings — a use that is well documented and celebrated. Whether comparable uses were made of the Belsize Park shelter is not fully established in the available records, but the general pattern of military appropriation of deep shelter facilities is clear, and Belsize Park was clearly within the network of facilities available for such purposes.
Post-War Fate
After the war, the Belsize Park deep shelter was maintained in a state of operational readiness as part of the Cold War civil defence infrastructure. The possibility of nuclear attack gave the deep shelters a renewed strategic rationale, and the government continued to invest in their maintenance and updating throughout the 1950s and into the 1960s. The Belsize Park shelter, like others in the network, was periodically upgraded with improved communications and ventilation equipment, reflecting the changing nature of the nuclear threat and the evolving requirements of civil defence planning.
The end of the Cold War reduced the strategic significance of the deep shelter network, and the facilities have been managed in various ways in subsequent decades. Some of the shelters have been let for commercial purposes — document storage, data centres, and similar uses that benefit from the deep underground environment. The Belsize Park shelter's current use is not publicly documented, and the tunnels remain inaccessible to the general public, closed behind the unremarkable concrete entry buildings in the streets above.
The deep shelter remains one of Belsize Park's most remarkable hidden features — a vast subterranean space of great historical significance lying directly beneath the everyday life of the neighbourhood, unseen and largely unknown to most of those who walk above it. The approximately one kilometre of tunnels, the engineering achievement of their construction in wartime conditions, and the varied history of their use represent a significant chapter in NW3's story that the surface landscape gives no indication of.
*Published in the Hampstead Renovations Heritage Collection — exploring the architecture, history, and stories of London’s most remarkable neighbourhoods.*