Where is this location in the film, 'Clouded Yellow' (1951)

[john]

TV recently had a rare showing of the 1951 released film, 'The Clouded Yellow' starring Trevor Howard and Jean Simmons. The finale of the film was filmed on location in Liverpool on a railway track (not main line) running parallel to some docks. In one scene a small pannier type steam locomotive (No 4 ) was seen bearing the letters MD&HB. Another small loco (No 21) also appeared briefly.

Has anyone any idea of the exact location, and what did the letters on the loco stand for?

Could be Mersey Docks and Harbour Board