I live in a building converted into flats, on the basement level there is an electrical cupboard which I believe should have fire rated doors and frames. There is also a full size cupboard which contains the water stopcock for each flat, there is nothing else in this cupboard. These cupboards are on the communal corridor for 2 flats, which do have other means of fire exit.

Should the water stopcock cupboard have fire rated doors and frame.

No, what would be the fire risk?

If it's just water & soil pipework and is fire stopped where required (e..g between floors) then it can be argued they don't need the same protection as the electrical cupboard.