I Was Monty's Double (film) - Wikipedia

1hr 39mins
Dir: John Guillermin
Starring: John Mills and Cecil Parker

Prior to the D-Day landings, an actor is hired to imitate Montgomery so as to confuse the Nazis

The screenplay for this war-based drama was adapted from the autobiography of M. E. Clifton James, an actor who pretended to be General Montgomery as a decoy during the Second World War. The film features opening scenes at London Liverpool Street station with John Mills arriving on a train hauled by an ex-LNER B17 Class 4-6-0. The shot has been edited, but the complete out-take appears on Video 125’s Steam on 35mm DVD and reveals the locomotive to be none other than No.61606 Audley End. What is really odd is that the loco was repainted into LNER colours for the film, so if this effort was made, then it seems very strange that the shot was edited in a such a way that the loco was no longer identifiable. In the following scenes shot from the footbridge, the rear of an unknown tank loco can also be viewed, as well as the tender of another loco in an adjacent platform. The later scene filmed onboard a train was very much a studio set, with the ‘back projection’ showing nothing but passing countryside.

On the platforms at Liverpool Street with ex-LNER coaching stock in the platform in BR carmine & cream livery
John Mills exits the platform. One presumes that the steam is emanating from No.61606 Audley End
John Mills has now reached the footbridge. This view shows to good effect what a fine station the old Liverpool Street once was.
In an effort to remain unnoticed, Ronnie Stevens turns away from the camera. In the platforms below one can make out the rear of an unidentified tank loco.
As Ronnie Stevens walks off we get a final glimpse of the station with a couple of empty platforms