The houses in the background of the OP don't look very British.
actylene lamps. Ironic on an electric loco
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just a thought......were any of the WWI trench railways electrified? That design has all the hallmarks of a cheap military austerity lash-up and would be eminently suitable for working over rough narrow gauge track. My guess its an ex-military locomotive pressed into post-war commercial service on narrow gauge during rebuilding. It would explain the tram-like features and also the Crown Copyright label.
I agree. I'm thinking the same about the other features and structures.The houses in the background of the OP don't look very British.
I thought first of Belgium too. Or perhaps Alsace Lorraine?. . . it could be Belgian or that part of northern France near the Belgium border.
Hellingly Hospital Railway in Sussex was my first thought, but loco body is a bit different.