Ok. I do quite a few bathroom refurbs, I have come across similar issues. Any new work obviously has to comply with the current regulations. The obvious solution, is to rectify by replacing CU, installing a smaller CU, partial rewire or full rewire.
As most customers have their dream of installing a flashy new bathroom suite, tiled floors, monsoon shower, they haven't it seems the money to spend on bringing their electrical installation up to an acceptable standard, or choose not to. One perhaps can understand their mind-set, they just want a new light in the bathroom, not the whole house rewired!
I recently did a bathroom refurb, where the customer wanted new down lights, extract fan, illuminated vanity mirrors etc. That was until I found out that the property had no lighting cpc. He did not want to pay for any alterations, so instead I only replaced the bathroom batten holder with a Class 2 fitting.
Another customer, who was having the kitchen & bathroom refurbished, and the CU did not have RCD protection for the lighting circuits, opted for a rewire & CU replacement. Their decision was made easier, by the mass of DIY alterations, IR faults, green slime present in most of the circuits and that the whole property was being refurbished.
Quite regularly, when only the lighting is being altered, I use a local RCD FCU, as a relatively simpler alternative, to no lighting RCD protection.
So it does take a bit of thought how you can achieve a satisfactory install, and you need to talk to your customer first, about the issues. Let them decide on how much to spend.
