1. If this were to be made into a film what would the main character be like?
Middle aged male gives impression of being non-descript average height and build?
Maybe slightly balding. Tall and stooping?
2. What clothes would the character be wearing?
Seems to be detective in wartime London should be wearing suit and hat if outside. Grey colour as he seems not to bother about form over function.
3. What furniture is in the main area in which the action takes place?
Strictly functional chair and desk lamp or fan filing cabinets for paperwork. Telephone. Perhaps some pictures on the walls but related to work.
Collect visual reference for the items on your list
I use google search for this era.
I have chosen the word “Eerie”.
My picture is of a middle aged man, who looks a bit older and has just left his desk. The desk is large and black, maybe he is doing some thinking about some case on the way to the windows. Maybe he is trying to find some clues to inspire him. Files of paper are on his table, the bleakness of spring sunshine has made him keep his overcoat (grey colour) on. His hat is hanging on the wall.