Modern steel shell, cast iron, fibre glass/ GRP shell (70's or early eighties)
A shell ( the bit you see) may be replaced at any time due to damage, corrosion or expansion
Well as you can see in this image
we currently have two cabinets, the one on the right is to replace the old one on the left due to loads of line faults so I was told.
Not been round there in a while due to health reasons, so the old one may of been removed, not sure.
But looking at the one on the left in the image it doesn't look that bad to me apart from the odd bit of rust, so maybe its down to all the line faults its been having as late along with needing more space etc.
Also if you look carefully you can see cabinet 39 across the road (just in front of the council truck) which is the same as the new PCP cabinet replacing ours.
TBH I prefer the old cast iron cabinet due to if a car hits it the car is worse off, whereas the new ones just gets squashed and end up half a mile down the road.