"Mizter T" wrote

Most interesting. But what is the line in a tunnel that appears to lead
from Holdborn Viaduct Low-level station under Smithfields meat market
to Aldersgate (now Barbican) station?

This spur was opened in 1871, and the LCDR agreed with the Metropolitan to
run at least 80 trains a day over it into Moorgate Street. These trains
usually ran empty, as the main business district was south of Moorgate
Street, and passengers found it quicker to leave the train at Ludgate Hill
(or Snow Hill) and walk to their offices. These trains were withdrawn from 3
April 1916, after which the spur was abandoned.

Peter