I am sure the isolator can be under the sink in the kitchen, and to be frank if the light is non metallic and suitable for outside I would not be over worried, but it is however you want to think otherwise a bathroom, and installing a bathroom in a new location comes under LABC so planning permission etc. I got caught out with mothers wet room, I had not realised how much was involved, so all the t's need crossing, and i's dotted as some official is going to inspect.
For example I had to install an extractor fan, once the completion certificate issued it was turned off and never used again. But still had to fit it.
You can change the use of other areas without a problem, a bedroom can become an office etc, But kitchens and bathrooms is a whole different kettle of fish, I left it to the builder, and all was great until builder ran off, and I tried to take over, it seems the builder is not required to ask for planning permission, the owner must do that, although builders often do it for the owner, I just don't want you to fall into same trap as me.
Seem to remember either BS 7671 or the on-site guide goes into the earthing arrangements. But my versions are out of date, so you need to check in an up to date version.
