Phil Clark wrote:
I noticed the other day that on the gable end of a building on Warwick
House Street, by the junction with Cockspur Street (and opposite the
Two Chairmen pub) there are the word "Grand Trunk Railway".

Does anyone know what this was, and was it a London railway, or was
this the London office of a national or regional company?

There was a North American railroad called the "Grand Trunk Railway"
(not all railway companies in North America call/called themselves
"Railroads").

Adam