Yes, a good point. A picture paints a thousand words!
Actually, the red, blue and yellow wires remind me of the old three-phase cables. I think they are now grey, black and brown (?) for some reason - probably to ‘harmonise’ with EU practices!
Looks like 3 core was used in this case, red will be live blue and yellow will be the switched lives, the yellow wire is for the other light hence the need to link the red to the common of the other switch , if the yellow is not used that’s OK , it just means the other switch won’t be used
And it suggests that there is no earth. It is an important question.
Yes it is EARTHED…
I beg to differ. It may be an earth or it may be a switched live.
The words ‘tucked into the back’ do not make the matter clear.
If the yellow wire is, in fact, ‘tucked in the back’ and not connected to anything, it is likely to be a switched live.
It the yellow wire is attached to the back box with a screw, it is likely to be an earth wire.
This is why a picture is important - for Lindyloo’s safety.
Hello Hello
I’m just back from the local rave - Essence of Motown - and found a message from Mags, who suggested I upload a photo on my profile page…which seems hugely easier than including it in a post…thanks Mags. So… I’ve put the photos I took into an album, cunningly labelled “Wiring!”…
The yellow wire certainly seemed connected to something, but I can’t say I definitely saw it screwed down!
Thanks, Lindyloo.
I’m afraid that it is not possible to see from either of the photos where the yellow wire goes.
For your own safety, I’d get an electrician to check that out.
If the back box is properly earthed, that’s probably OK. If not, you are putting yourself at risk.
It would also be sensible to check whether there is an earth wire at the light fitting. If there isn’t - which is not uncommon - it is perfectly safe as long as you don’t use a metal light fitting.
Until things are checked, please avoid touching the metal screws of the switch plate, and if you have a metal light fitting avoid touching that as well. Follow those simple instructions and you will be safe, but please check out the earthing arrangements, if any.
JBR - I’ll make sure someone checks the switch soon - hopefully that electrician will get in touch next week.
Thanks for your concern and advice - it’s greatly appreciated. L x
No problem.
Nice hat, by the way!
Isle of Wight Festival Hat 2016… 
Righto , just looked at the pics it seems to me that the yellow wire was for the other switch, ( light) and had become disconnected , was this the cause of the sizzling noise, ? As lindy pulled the sw off did the wire finally break appearing to be just sat in the back? , is there a green/yellow wire connected to the metal sw box ? If the yellow wire was used as the earth?, if so it should have a green/yellow sleeve and be screwed into the back box, hmm, I think lindy doesn’t need an electrician, she needs sherlock:-D, there’s probably a joint box somewhere, where the wires could be traced , but I think that’s a job for a sparky, if there’s no earth at the back box , a new cable may have to be put in, I doubt there’s enough slack on the existing cable to remake it
An easier and cheaper alternative would be, as I suggested, replacing the metal screws attaching the plate to the wall with nylon screws.
This would make the switch safe.
Also, as I said, if there is no earth connection at the light fitting this, too, could be acceptable provided no metal light fittings are used.
Although the ideal would be to have full earthing at switch and fitting, there must be many properties where this is not the case, especially older ones, and it is still considered legal and safe.
Ask your electrician. He will probably agree.
Not if you install a macerator. 
I could have that turd running behind your TV, around your kitchen then upstairs to do a circuit round your bed then empty into your Ladybird slippers
I see what you mean about the earth JB, after carefully
reading Lindy’s post again I can see that the yellow/green wire was only described in the book and not in the fitting…Should have gone to Specsavers…
But it must have an earth connection to the metal backbox, I have in the past visited a house where the whole wall became damp and live from a faulty socket.
Ideally, yes.
Lindyloo, I’d be interested to hear what the electrician who installed the switch has to say about this.
Even six years ago, there were rules about earthing arrangements.
It could be that installing an earth wire now would involve lots of chasing out the plaster and re-wiring that particular supply.
On the other hand, it could be that the yellow wire could be traced back from whence it came and, if possible, disconnected at that end. It could then be re-connected appropriately and used as an earth wire.
The other concern is that, if that supply doesn’t include an earth, what are the other circuits like? That could mean a full electrical survey and that, in turn, could lead to expensive rewiring.
It’s a choice. Either keep what may be a safe arrangement, though perhaps not ideal by modern standards, or bite the bullet and have a lot of work done - IF it is necessary.
The yellow wire in all probability was to a wall light somewhere that has been disconnected? hence the two-gang switch. No need for nylon screws, if you check the photos you will see that the back box has plastic/nylon screw-fixing lugs. That means the wiring is around 45 years old so generally will not have an earth within the cable. This presents no problems provided that ALL switches and fittings on the circuit are plastic.
Ah, I didn’t see that. Now you mention it, those are not metal lugs after all, so it’s probably OK. I assume the new switch you’ve put on is all plastic, Lindyloo, so that’s probably OK.
I’d do what Judd says, though, and check that all of your switches and light fittings are plastic.
Always remember…Red to Red…Black to Black…Blue to bits…
Seriously, though, I have always thought that our colours: RED, BLACK, GREEN, were far more logical and easy to understand than BROWN, BLUE, GREEN/YELLOW.
I won’t go into the whys and wherefores, though. People must be fed up with hearing about the EU!