The machinery in the picture was used for grinding and polishing mirrors for telescopes. Here's a history of the bunker:
Construction & World War Two.
Either during, or slightly before the war, Surrey Council drew up plans for at least four deep underground shelters. A plan from their Highways and Bridges department revealed that the Brighton Road, Coulsdon shelter was the fourth, situated on the A23 Brighton-London road, within the grounds of Cane Hill Mental Hospital and within easy reach of a new suburban housing estate across the road.
The other deep level tunnels were believed to be the Ashley Road tunnels in Epsom (which have a similar layout), another unspecified tunnel system at Epsom Downs and some form of underground shelter at Godstone Road, Kenley.
The planned layout for the Brighton Road tunnels was simple and functional. Three parallel longitudinal tunnels would be driven into the chalk hillside, with four parallel lateral tunnels connecting them. Spoil was to be piled onto the hill above the tunnels to provide extra protection from bombing, whilst more soil was heaped in front of the three tunnel entrances to provide a blast wall. Three offset entrances then connected these entrances to the car park adjoining the A23.
Two other longitudinal tunnels would be dug as toilets, whilst inside the tunnels a small sick bay and canteen were planned.
The plan was over ambitious and the tunnels actually dug are a poor representation of the plan. Two of the longitudinal tunnels were abandoned, stopping short in a sheer white wall of chalk whilst only two lateral tunnels were completed. A mysterious new room was dug to the north of the tunnels – not shown on the plans – whilst the canteen was never excavated.
The total cost of the four shelters was £71,000 at 1943 prices – and all were owned by the London County Council. Perhaps the Brighton Road tunnels were never completed.
The wartime use of these shelters is also in dispute. Whilst it wasn’t in any doubt that these were public shelters, rumours circulated that the Canadian Military used for the tunnels for storage. Given that the saturation bombing expected didn’t hit Croydon and Coulsdon, and that most householders had their own shelters, perhaps the tunnels were found to be poorly used and therefore available for other uses.
More credence to this story was given by the owners of the optical factory who discovered war time reconnaissance photographs of Berlin in the tunnels whilst converting them to a new use.
Immediate Post War
After the cessation of hostilities, the various bunkers and shelters (all still owned by the London County Council) were mothballed but several were reconsidered as potential nuclear shelters. Surrey County Council resurveyed the tunnels and the deep level shelters were again considered useful. (In this list, Brighton Road and the two Epsom shelters were joined by Riddlesdown Chalk Pit in Purley).
It is probably from this potential reuse that the nuclear shelter rumours sprang.
Cox, Hargreaves and Thomson, Limited.
Now sitting empty, Brighton Road tunnels were given a new use of life by Cox, Hargreaves and Thomson, Limited. They manufactured lenses for the huge telescopes used by observatories and required a location which had constant temperature (so that the glass would not expand and contract whilst being ground and polished) and long rooms where the focussing of the lenses could be tested. The tunnels were perfect.
The company made several small changes to the layout of the tunnels after taking over in 1949. The southern entrance was bricked up, whilst the central tunnel was concreted over, so it continued uninterrupted through to the car park. The southern tunnel had its dog leg removed, so it exited straight out into the valley behind the blast wall.
The ‘sick bay’ required reconcreting, and at this point the tunnels were rewired, with modern fluorescent lighting and power points being installed throughout the network.
Whilst the tunnels were extremely suited for the production of extremely high quality lenses, they took their toll on the workforce. It was very cold and damp – water would condense in the electrical conduits causing the power to regularly short out. Obviously annoyed by these constant electrical brown-outs and the subsequent risk of shock trying to repair the sodden fuses, the company came up with a typically British cheap and cheerful solution.
A fridge was taken down into the tunnels and wired up backwards. Thus, acting as an air conditioner, it was placed near the ventilation hole at the back of the tunnels, and water was allowed to evaporate out of the tunnels up the chimney.
Some tales of working in the tunnels by the employees of Cox, Hargreaves and Thomson, Limited can be found in the tour section. And many of the intriguing custom French made pieces of machinery which were used as lens grinders and testers can be found scattered around the tunnels.
But working in the cold and damp conditions of the shelter was asking too much and the optical works left the tunnels in the 1970s. Employee Norman Fisher last visited the bunker in 1975-6, and found the lights inoperative, the door partially jammed and the machines unuseable. Cox, Hargreaves and Thomson, Limited was wound up on the 12th October 1978.
Garage And Dump
It seems that a garage/workshop took over the tunnels, being primarily situated in the southern longitudinal tunnel. Partitions, tool racks, and all sorts of rusting car parts in this part of the tunnels points to their new use. (They probably had to unblock the southern exit to get all this machinery and hardware into the tunnels).
Given the number of garages and repair units on the eastern side of the A23, then it’s not unlikely that an enterprising garage owner took on the tunnels as an extension to his business.
But the same problems that dodged Cox, Hargreaves and Thomson, Limited probably plagued the garage workers. It was cold and wet and everything brought down into the tunnels would start to rust. It was not an ideal environment.
One night in the 1980s, the son of an employee of Cox, Hargreaves and Thomson, Limited paid a moonlight visit to the tunnels for a nostalgia trip. He observed groups of men dumping all sorts of miscellaneous bits and pieces in the tunnels. It was probably these men who left the remains of the telephone box, the tractor wheels and the railway semaphore here.
Probably because the tunnels were now derelict and being used as an unofficial public tip, the tunnels were swiftly sealed by bulldozing huge banks of soil through the three tunnel entrances. And so they were left, gradually being forgotten - but the stories started to circulate.
Cane Hill Hospital
Rumours also circulated about the connection between the hospital and the shelter. The most common was the use of the tunnels as storage by the hospital - the old weird machinery used by Cox, Hargreaves and Thomson, Limited was often mistaken for strange medical contraptions.
One story that refused to die was the suggestion that the tunnels were a mortuary for the hospital. This is untrue – the tunnels were built as a public deep level shelter and were designed (if not constructed) by Surrey Council’s Highway and Bridges department. The only reason for suggesting this connection is the close presence of the hospital itself. Plus Cane Hill had its own well equipped mortuary, out of site at the back of the hospital – the Brighton Road tunnels were too far away to be of use. But given the repeated references of Cane Hill Hospital, and refutations of any involvement, it’s perhaps ironic that the Land Registry now cites the hospital as the owner. This probably indicates that the shelter was built on land owned by the hospital, requisitioned under wartime planning. After disposal of its assets, the ministry or official body holding the shelter and its land would’ve given it back to the original owner.
However, the shelter was used by the optical factory and a garage repair workshop. Perhaps they merely paid rent to the hospital? I’m sure these questions will be answered in the fullness of time.
The Future
The Cane Hill site was recently sold and it isn’t known what the new owners’ plans for the tunnels are – indeed it isn’t known if the new owners know of this part of their acquisition. The tunnels also escaped being buried under the new Coulsdon by-pass – a swathing new road which cuts through the lower borders of the hospital. Deep Shelter Number Four continues to survive – but for how much longer is anyone’s guess.
More can be found on my website:
http://www.simoncornwell.com/urbex/projects/chb/index.htm
All the best,
Simon
Thankfully I didn't meet any hate and rage filled man who expressed a wish to disembowel me down there. 
I listen to a huge range of stuff but mostly industrial. 
