One of my downstairs lights is on the upstairs light circuit

Hello folks,

I've just discovered that the pendant light in my downstairs dining room is conected to the upstairs lighting circuit, and switches on and off with the upstairs light circuit MCB.
I've not touched, any of the light circuits and so can only assume this was done by a previous occupant ( we are the 5th family to own this house) or maybe ( doubtful) at the build stage.

There are obviously some safety implications to this discovery.

I have found some square junction boxes in a roof void that are marked up with lighting circuits, and full of chock blocks, but it looks like a bowl of spaggetti and i don't want to meddle with it. Lighting switch circuits look like a nightmare at the best of times even for simple circuits.
Would it be OK for the moment just to put a suitable warning label inside the single light switch and ceiling rose.

I thought the wiring circuits inside the aeroplanes that i work on are complicated, but at least the individual wires are hot stamped with idents and all of the multi-pin plugs are idented too, this is just a nightmare, 20+ year old pencil marks written on the grey sheaths just don't cut it .

It would make sense to put a warning attached to the consumer unit for anyone working on the system, just hope they have used the neutral for the up lighting too!!

And of course the bright black on yellow label tape in my label machine had to run out right now didn't it

I've lived in this house for 8 years now and am surprised that this is the first time i've had cause to notice this so I've done a full lights check.

I also have an outside light above the back door that is also connected to the upstairs lighting circuit. It is controlled by a 2 gang switch by the kitchen door though, so one switch operates the internal downstairs kitchen light on the downstairs lighting circuit and the other switch operates the outside light on the upstairs circuit - hardly ideal.

Might get the DVM out and have a little look-see for anything obvious, it is bugging me now.