This is my cue.......
In the 14th A.61 said, of switches in bathrooms:
Where Reg D.17 requires a switch to be situated so as to be normally inaccessible to a person who is using a bath or shower, it is admissible for the switch to be placed in a suitable position outside and immediately adjacent to the normal access door of the room, or to be of the type operated by an insulating cord.
D.17 said:
Every switch or other means of control or adjustment shall be so situated as to be normally inaccessible to a person using a fixed bath or shower.
Exclusions:
Shaver supply units installed to reg D.19
Insulating cords of cord operated switches
In the 15th 471-39 said, of switches in bathrooms:
Every switch or other means of control or adjustment shall be so situated as to be normally inaccessible to a person using a fixed bath or shower. (Does that sound familiar?
)
Exclusions:
Shaver supply units installed to reg 471-37
Insulating cords of cord operated switches
Controls incorporated into instantaneous water heaters to BS3456
Switches of SELV circuits complying with reg 471-39(a)
So, basically, the 15th suggests if you had a bathroom where the switch was inaccessible from the bath, you could use a plate.
The 14th does not mention this, but offers the option of a pull-cord.
This is where the idea that you must use a pull-cord comes from (unless you put a plate outside).
That and the latter-day trend for fitting pull-cords in all bathrooms/ toilets/ cloaks because it is "safer".