Just found this on the same site, also online until 9th august.
Documentary of a night in the life of the London Underground, filmed in 1958 by British Transport Films, following the 800 night-shift workers and includes the discovery of a broken rail in the middle of the night.
Thanks to A for linking me to this, It will be online until the 9th August.
Documentary programme about days and nights in the life of London's Angel tube station, from the daily round of fraught commuters and overburdened lifts to the troglodytic nightlife of track cleaners (fluffers) and the track maintenance men collectively and descriptively known as the permanent way.