I've seen the c.p.c. reused as a live before- usually where someone tried to convert to 2-way switching but didn't want to disrupt the decor by changing to a triple and earth. I wonder if the switch was a 2-way one in a previous stage of the installation's life and then converted back.
We're about to take you to the IET registration website. Don't worry though, you'll be sent straight back to the community after completing the registration.Continue to the IET registration site