Watch Secrets of the London Underground Season 3 Episode 4 Online

Tim and Siddy embark on a night-time track walk to the abandoned station of British Museum. The pair discover enormous 1930s hand-painted adverts and evocative white tiling. During the second world war it served as a shelter and spine-tingling clues to the children who stayed there during The Blitz can still be seen. Siddy visits the elegant, white-stuccoed houses of Leinster Gardens, which are hiding a stunning secret of the London Underground behind their walls. These aren't all real houses at all, they are in fact, an incredible quirk of the Underground's history of steam.