NML - The Transport Shed

The tunnels below the River Mersey are of interest to underground train scholars and historians because the service originally used steam locomotives ... but it became bankrupt because the tunnels were so unpleasant from the smoke that passengers actively avoided it*. Quite possibly the same would have happened in London had the deep level tube trains used steam traction for their passenger services - at least London's subsurface tunneld were partially ventilated.

*After bankruptcy the tunnels were bought and converted to electric traction, and the service then became so successful that it is still open today, as a part of the Meyseyrail Wirral line.

Also, another London Underground connection is that during WW2 withdrawn Metropolitan & Great Western Railway electric trains which were built for the service to Hammersmith were sent to Merseyside in case of air raid bombs destroying the Mersey Railway rolling stock. As far as I am aware the Met & GWR trains never actually carried fare paying passengers in Merseyside.