Conventional practice would dictate that the CPCs of any circuits introducing power into a bathroom would be included in the rooms equipotential bonding.
However I have to admit to not being able to think of any logical justification wrt to a lighting circuit where light is supplied by 12V downlights (i.e. no earth to the metalwork)) fed from a SMPS/transformer concealed within the ceiling void, and with a plastic cased pull switch in zone 3. Hence there is no way for someone to ever make contact with anything connected to the lighting circuit CPC. Can anyone think of a reason to include the CPC in the bonding in this situation?