I am about to install a grab-rail and cabinet, both of stainless steel,
in my bathroom. My query is whether they should be included in the
equipotential bonding.

BS7671 is not specific in this regard. It lists examples of
extraneous-conductive-parts that must be included, and also some that
need not be considered, but offers no definitive list or
characteristics. The OSG includes "metal handrails"in the examples
of items that do not need to be bonded, but this is not mentioned in
the examples in the regulations themselves.

My view is that as these items will be isolated from earth and as there
is no foreseeable single fault condition or circumstance that would put
them at an electrical potential relative to earth (for all practical
purposes), then bonding is not necessary.

CRB