Watch Ian Hislop's Trains That Changed the World Season 1 Episode 2 Online

The London Underground - first operating in 1863 - changed the way people get around cities forever, driving travellers deep underground to clear congested streets. Ingenious technology, from electrified tracks to tunnels under the River Thames, has gone on to influence railways worldwide. This edition reveals how the filthy and crowded streets of London were transformed by the rapid expansion of the Underground