I have an old consumer unit (Wylex) with rewireable fuses.

If I decide to replace it, will I be required to use RCD/RCBOs on all
circuits (either one 'whole house' RCD, or one per way)?

Currently, there's a single ring serving the whole flat (approx 85
sqm) and a recently installed ring serving the white goods in the
kitchen (replacing a spur bodged in by a previous occupant). Given a
fair number of switch-mode power supplies on the main ring, I'm
worried that it'll exceed the leakage budget. Would a better technical
solution in that case be to replace all the sockets on the main ring
with RCD protected sockets, is that allowed/necessary under 17th ed -
or is all this unneccesary and the lack of RCD protection
'grandfathered' in?

With my luck, I should probably have replaced the CU when I had the
chance before the 17th ed came into force.

Cheers (or maybe not)

Sid

(Oh, and sorry for being strictly off topic - I won't be replacing the
CU personally - I don't have the appropriate test equipment available,
and more to the point, even if I hired it, I don't have the knowledge
to use it properly)