How about this:
You get a call, the guy installing the new smart meter has told someone their old Wylex 3063 fuse box is illegal and they need a new Fuse box.
Not an RCD in sight, no CPC on either lighting circuit and they have a brass 5 lamp chandelier thing in the living with a brass Heritage rope edged light switch, a couple of metal fluorescent light fittings in the kitchen and a chrome shaver socket in the bathroom.
They don’t want the place re-wired, they don’t want to replace the metal fittings with plastic, they just want a new fuse box.
Do you replace the CU and provide RCD protection for all their circuits, or do you walk away hoping nothing will go wrong?