I finally got to visit the Clapham South Deep-Level Air-Raid Shelter last Thursday as part of London Transport Museum's Hidden London. Some photos by me above. For more information see my Subterranean City or here. It was very well organised - quite a lot of walking is involved as it's vast.
Author of Subterranean City, Beneath the Streets of London, London's Coffee Houses, Decadent London, The Folklore of London, Subterranean City (Revised and Expanded Edition), Netherwood, Last Resort of Aleister Crowley, Lord of Strange Deaths, the Fiendish World of Sax Rohmer; Secret Tunnels in England, Folklore and Fact