I'm fitting a new consumer unit and the requiremnet is 16 sq mm for the
primary earth to the supply and 10 sq mm for the secondary bond(s) to
gas/water/oil. My place has a PME earthing which has the most stringent
requirements, other earthing arrangements may not.

Although the size of secondary bonds is specified in the wiring regs, I
don't think it specifies which kinds of work require an update.
Generally the regs don't apply retrospectively, so if no work is
carried out on that part of the system then there is no requirment to
update.

If building the conservatory requires the secondary bonds are moved,
then yes they probably should be updated.