I have 3 x 3-core cables coming into the light switch which are from the CU and to two lights. I also have a single red wire, sheathed in grey. Any ideas what that is? What should I do with it?

max, November 2009

I would try to find the other end by looking in the light fittings and other switches.
If the situation really is as simple as you have described it I can't see that it does anything, so should be put in a piece of terminal block, taped up and tucked away behind the switch.

Adam, November 2009

You say you have 3 cables at light 1 from switch and 2 from different lights? Is your light in bathroom? How many switches to switch on that light? and does it only switch on 1 light (or 2 lights come on together with switch)?

Raffelect, November 2009