Secrets of the London Underground is returning for a fourth series

A new fourth series of Secrets of the London Underground will be coming to Yesterday TV, and filming for the new series is underway now.
(c) UKTV
Secrets of the London Underground has quickly gained a loyal audience on Yesterday, reaching over 10.1 million individuals across all series to date, and is among the top performing Yesterday titles on UKTV Play.
The new series is filming now, reuniting rail historian Tim Dunn (The Architecture The Railways Built) and Siddy Holloway from London Transpo