... until about 1948 films were unavailable in the shops for amateur photographers.
I don't think that was the case. My father was a keen amateur photographer, and the pictures I've inherited include a number taken during his WW2 service (Army, Northern Ireland).
What does occur to me, though, is a question that might relate to the date and location: where were Cowan & Co based?
The original post says this was taken in Manchester, yet the truck has a Glasgow registration. So, were Cowans from Glasgow but delivering to Manchester? Or were Cowans in Manchester and using a truck that had been registered in Glasgow?
If the latter, that suggests the truck may have been secondhand when they got it, which might push the date of the photo on a bit. Or could the basic Leyland chassis have gone to a truck builder in Scotland, then been sold and registered there?
