We are changing the ceiling rose in our downstairs hallway, as it fits a stupid fluorescent bulb you can only buy online. DH unscrewed old rose and took it off, but then we had to go out. When it came to putting new one on, there is a spare wire!
We have 2 blue, 3 brown, a yellow/green and a brow one with sheath.... All normal, no problem putting them in the right place.
But. There is also a grey one. No empty "sockets" left so guess it has to double up somewhere, but where? None of the other roses in the house have this spare wire.
It does have a two way switch, but the other two way in our house does not have a grey wire in it.