"Graeme Wall" wrote

In Charles E Lee's The Metropolitan Line there is a photo dated Mar 1866
showing the widened lines in use at Farringdon. The tracks in foreground
are laid with mixed gauge track.

At that date the Widened Lines only ran from Farringdon to Aldersgate
(Barbican) They were extended to Moorgate on 1 Jyly 1866, and westward to
Kings Cross early in 1868. The Snow Hill link from Farringdon to Ludgate
Hill opened at the beginning of 1866, and the third side of the triangle
from Snow Hill to Aldersgate came into use in September 1871. Broad Gauge
GWR trains ran to Moorgate until 14 March 1869, but it is unclear whether
they used the original Met lines, crossed to the Widened Lines at
Farringdon, or even crossed to the Widened Lines at Kings Cross (from early
1868) - if there was actually a connection from the Met to the Widened Lines
at Kings Cross.

Peter