London's DEEPEST SECRET

We reveal what lies beneath the capital's streets

- KATE THOMPSON

Unsuspecting shoppers and commuters on a quiet south London street are oblivious to the fact that they are walking over history. Deep below their feet, hidden in the bowels of the earth, is a sprawling labyrinth of tunnels that saved lives during World War Two.

In 1944, as the beleaguered capital endured the onslaught of V1 rockets, popularly known as Doodlebugs, and V2 missiles, five deep-level shelters opened to provide refuge to 40,000 Londoners. And during the post-war years, the mile of subterranean passageways at Clapham South continued to provide shelter to people from across the world as a 'penny hostel'.

London Transport Museum is launching a season of its Hidden London tours, and one will take you through this eerily evocative network of tunnels, located 36m below ground.

'When the Blitz broke out on 7 September 1940, the Government came under increasing pressure to build deep level shelters, in addition to the Tube stations, far enough below ground to escape the horror of the bombs,' explains Siddy Holloway, the museum's engagement manager, historian and presenter. 'The need for this was escalated in October 1940, when over 60 people sheltering at Balham Tube station drowned in liquid slurry after a bomb hit the high street above and it breached the sewers.'

It was decided to construct extra tunnel shelters that were bomb- and gas-proof, and at least 60ft below ground. 'This shelter was built as a response to the tragedy, and finally opened in July 1944. It was one of eight shelters located on the Northern and Central Line at a cost of £3 million, a huge amount in 1944,' says Siddy. 'In the event, only five opened to the public, and the rest were taken over by governmental departments (American Military, British Military and Ministry of Information).'