For decades it has remained secret to all but a chosen few, its work highly classified. But now the underworld of MOD Corsham can be revealed. Oxford Archaeology has been investigating this secret defence complex, and has completed a characterisation study, giving us remarkable insights into its history – and a view of the Government’s underground nuclear bunker that was never used.

The vast labyrinth of interconnecting quarries and tunnels began life in the 1840s, and grew as the demand for the fine Bath Stone expanded. Remains of the quarrying history survive, including cranes and working tools left in situ as the quarry was requisitioned by the War Office.

The outbreak of the Second World War ushered in a new phase of development as quarrying activity ceased and the military potential of the resource was realised. Industrial production continued with aircraft manufacture, and the vast facility also provided storage space for the huge quantity of ammunition required throughout and after the war. The level of preservation of the ammunition depot within Tunnel Quarry is remarkable. Features include an underground railway, two platforms, massive generators and a conveyor belt system transporting ammunition around the 22 acres of storage space.

The global conflicts of the Second World War did not finish in 1945, but evolved into a new phase with the Cold War. The later use of the aircraft factory as the Central Government War Headquarters is symbolic of the mutual distrust between east and west. The Cold War brought the world to the brink of nuclear destruction, but had the high-stakes political manoeuvring failed it was to Corsham that the country’s elite would have retreated. Here was the last redoubt, the ultra secret bunker where the survival and restoration phases of nuclear war would have been conducted had Whitehall been destroyed.

Constructed 100 feet below-ground and surrounded by deep reinforced concrete walls this 34-acre complex had the capacity to house the prime minister, a nucleus of high officials and 4,000 staff. The complex was only declassified in 2004 and retains an excellent level of preservation. An extensive telephone exchange, kitchens, bakeries, offices, BBC studios remain in place, all housing an array of artefacts left untouched since the 1960s.

Oxford Archaeology is now undertaking a ‘values study’ investigating the myths and legends associated with the site and its social, economic and cultural impact. It will also consider the national and international value of the site’s components.