Jim Brown wrote:
If the Bank of England sacrificed its vaults (Very little use for them
now, with the gold sold off) and Cannon Street St was put underground
(Plus a new tunnel under the Thames), would a tunnel connecting
Moorgate and London Bridge be feasible? Or do the tube lines around
there make it impossible?

I seem to recall that in the post war plans for Londons Transport, one
of the new lines to be built was an extension of the Northern City line
from Moorgate, through the City and to new underground platforms at
London Bridge and linking with the Crystal Palace (High Level) branch
line of the SR.