There are examples in BS7671 that gives guidance as to what is allowed or permitted. It does not give guidance as to what is safe or unsafe.
I note from section 701, there is a description of zones 0, 1 & 2 and what and cannot be installed in those zones. There is no such guidance as to what or should not be installed outside of these zones, except 'socket-outlets are prohibited within a distance of 3m horizontally from the boundary of zone 1. There is no other guidance for what can be installed outside of these zones in locations containing fixed bath (etc) or shower, other than it does not apply to switches & controls which are incorporated in fixed current-using equipment for use in that zone or to insulating pull cords of cord operated switches.
Therefore one could install a plate switch outside of zones as it does not appear to contravene any regulation within BS7671. But that ordinary plate switch could be operated by someone stood in the bath or shower.
So IMO, 'the correct answer to that must be, that 'it appears that' it is allowed, but it is inherently unsafe'.