A bit of info for you:
Up till the adoption of metric brick sizes in 1965, mass-manufactured Scottish bricks were 3.25 inches tall (England had two imperial-standard sizes for mass-manufactured bricks - 2.625" tall and 2.875" tall)
Since we're in Scotland, and we're pre 1965, we can assume that each brick in the wall behind this box is/was 3.25" tall. There are ten courses of bricks visible behind the box and (possibly) a partial brick visible where the pavement has been dug up to site the box; each layer of bricks is/was bedded on a half-inch layer of mortar (again, 0.5" was the imperial standard for each layer of cement (10 mm thick after 1965)).
So, 10 courses of bricks = 32.5"
10 layers of cement = 5.0"
Bit at the bottom, approx = 2.5"
Total height of wall to underside of coping stones therefore is approximately 40".
Based on that:
Note, the dimension of 40" for the upper portion of the box is the minimum - this is a single photo which has some lens distortion. Including the pitched roof but not the lamp, we have something a little over eight feet tall. Effectively, this box is the same size as the as the red - contemporaneous, Gilbert Scott K6 telephone boxes so beloved of filmmakers!
Does that help?
T