Around the time of WWII Surrey County Council commissioned the building of four deep shelters, Coulsdon Deep Shelter was the fourth and was built within the grounds of Cane Hill Asylum. After the war, the shelter was purchased by Cox, Hargreaves and Thomson, Limited who specialised in the manufacture of optical devices – mainly lenses for huge telescopes. They purchased the tunnels as it provided the ideal atmosphere for the production of the lenses – a constant temperature meant that they did not expand or contract during the grinding process. However, the main drawback of the tunnels was the cold and damp conditions within them, this played havoc with corroding equipment and the moral of the workforce. To combat this, the company brought a refrigerator and wired it backwards so that it could act as a crude air-conditioning unit.
Cox, Hargreaves and Thomson finally left the tunnels in the early 70s and the company subsequently wound up in 1978. After this they were used as a garage for a small length of time, but abandoned again because of the same problems faced by Cox, Hargreaves and Thomson. It was the later used as a dump for old VW car parts and the tunnels were then sealed by the local council.
British Pathe made a documentary on the Telescope manufacturers that occupied the tunnel after the war, it can be viewed here: British Pathe Films – Telescope Makers