I wish to concur that, this new series of Secrets of the Underground has reached the perfect balance of reaching both a general audience, together with maintaining the interest of a more specialist rail enthusiast one.
The Waterloo & City Line episode was very interesting - I've always liked the OVS Bulleid inspired 1940 stock and remember riding them back in the 1960's, when still in British Railways SR Green livery. Other things I recollected at that time, was the novelty of the Travolator; lack of a suicide pit between the tracks at Bank Station and; only a third rail! Lastly, I was amused back when the same stock was repainted into British Rail Blue, the carriage end metal ventilators, which had originally featured integral letterwork stating 'Southern' and 'Railway' on each side - then, the latter was replaced with a new part now stating 'Region'! Must get it right!
However, the episode featuring King William Street and the City & South London Locomotive and Padded Cell Stock was very educational. As well as the very short life of the City terminus, I believe it had been a major oversight to by pass and exclude an interim station at London Bridge to serve the SE&CR/L&BSCR Station there. Although, I understand the new tube railway couldn't reach an agreement with the Main Line Railway, when originally constructing, for such an accomodation?
Lastly, I didn't realise Knightsbridge Station was being upgraded further with more entrance and exits at the original station end. I thought the Hans Crescent passageway, entrance and exit added in the early 1930's, covered all of the local bases, being done to minimise the inconvenience and facilitate the closing of the fairly close by Brompton Road Station? I must revisit the station soon to reorientate myself of what's being added/changed.
