Hi
Putting a note on the COC will make the COC invalid and not worth the paper it is written
On an existing installation it would need to at least comply with 5.3.8

5.3.8 Positioning and accessibility of electrical equipment
Electrical equipment shall be so positioned that
a) it does not impair the functioning or safety of other equipment,
b) it is readily accessible for installation, replacement, operation, testing,
inspection, maintenance and repair (see 6.6.1.9 and 6.9.4 for the main
switch). All parts of the installation shall be accessible without the need to
enter any adjoining premises (for example, in an apartment building),
NOTE Common areas (such as passages and entrance halls) are not regarded as
adjoining areas.
c) there is easy access to its location
d) it is not likely to be physically damaged,
e) dust or moisture is not likely to accumulate on live or other parts and cause
flashover, and
f) where the distribution board is concealed by a cupboard or other covering,
the notice for live electrical apparatus referred to in annex O shall be in a
conspicuous place indicating the position of the distribution board.