I seemed to have already answered this question but did not notice bathroom which means unless like for like you need to inform building controls under Part P. I would guess switch wire which is often black has been put with the neutrals also black instead to connecting to lamp.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!