I recently had an electrical problem where a short on a lighting
circuit in the loft caused my radiators and water taps to become live.

Obviously the plumbing is inadequately earthed, which I will remedy.
Additionally, a short-circuit tripped my (very old) trip switch. I
called an electrician, who sucked air through his teeth and told me
that all of the old rubber-insulated wiring in my house (both lighting
circuits and one ring main) would need to be rewired. He also took out
the fuses from the lighting circuits (which he said were reading very
low insulation levels), and fitted a 30mA RCB for the entire house.

I am wondering whether he took the best course of action. Might my old
rubber-insulated wiring still be serviceable? If so, could I simply
rewire the shorted/failing sections (which are in the loft and easily
accessible)? I'm worried that if I try to do this, my old lighting
circuit will not work with the newly fitted 30 mA RCB.

Will such a repair be possible, and if so, what are the risks
associated with it? Will it be safe?

Will a qualified electrician undertake repairs like I've described, or
will they require me to rewire the whole house!?

Will a house with (functional) rubber insulated wiring pass an
electrical safety inspection for e.g. renting?

Thanks for any help or advice.

Best wishes

Harry