In the process of removing an over-sink light and shaver outlet I
switched off the ceiling switch (I presume there used to be a light
fitted that did not have an integral switch), the light went off so I
was about to get to work but something made me check first. Long story
short: inside the ceiling switch the red wires were joined and the
blacks went to the switch (one of them had red sleeving on it) resulting
in neutral switching and a permanently live feed to the light! I'm
getting a bit blasé in my old age so this near miss is a good reminder
to check!
I've just stripped the paper underneath where the light was and someone
has written "live!" on the wall - presumably, 20 years ago they got the
surprise that I narrowly avoided today.