Picture dump!
I happened to be near to this box this morning, so while in the area (and completely unprepared) I quickly rattled off some pictures.
I'll be honest that when I saw it I was a little disappointed, seeing just a brick building, as your mind briefly tells you "It's a police box - it'll be blue and look like the TARDIS" even though you know that there were so many variations around the country and that this isn't the first brick box that still exists. On the plus side, being now a nondescript brick building means that it is hidden in plain sight - I doubt that even the locals know what it's previous purpose was. But on the 1950's map it says it's a PCB (Police Call Box), so that's what it is.
Anyway, pictures...
The box is brick built. The doors on the front appear to be a later addition. There is a boarded up door on the left side of the box, and a bricked up panel on the rear of the box (which I have highlighted in green). The roof appears to be a flat concrete slab.
As expected it has been covered in graffiti, and the area to the side and rear of the box is overgrown so I was not able to get a decent picture of the side door. There were also lots of bottles of what could only politely be described as second hand water lying around the area (I must have counted at least 30) so I didn't want to hang around too long.
The addition of the front doors would appear show that in its later life the box has been repurposed, possibly several times, as the doors do not look original. With its proximity to the swimming pool I could well believe that this was repurposed, possibly in to a kiosk selling refreshments, before later being turned in to storage.
I didn't have a tape measure or meter rule with me, so used the measurment app on my phone (so the measurements won't be exact, but would give an idea). The measurements are (in feet, sorry):
Width: 10'
Height: 7' 6" (to the bottom of the roof)
Depth: 13' 7"