I've uploaded an image which will hopefully make this question easier to understand as it shows the wiring as it is currently and shows what does and does not work with regards to the switches.
This is how the wiring was when i purchased the house and the switches have never worked but i assume there must be a way of making them work or single switches would have been used!
I'm hoping to have what would effectively be a 2-way switch for both the upstairs and downstairs lights but the only way I know of doing this would involve more cables than i have available so is there a way of doing this without the need to run more cables (using the cables i have available) is really my question?
Left picture 2 + E the black wire should be line when the left hand switch is on, the left hand switch is on/off only with L2 not used. The 3 + E will go to up stairs switch, L1 is always live, and L2 connects to the light the com will swap as show with diagram I posted on other forum.
Right picture, left hand switch is two way, one of the cables should go to down stairs the other to lights up stairs since cable going to down stairs switch blue should be always live and only that cable should be connected to com then the right hand cable should go down stairs and the left hand cable red is always live, blue goes to two way light and yellow to some other light.
So there seems to be nothing wrong, that should work, so you should have one two way and one on/off at both switches.
To get a second light working as two way there are two methods, one as you say needs another wire, the other needs wireless light switches, I see a red wire on the 2 + E unused if this can me made line from the same supply as used up stairs then you could have a second two way system, however if the down stairs and up stairs lights come from independent MCB/fuse/RCBO then it can’t be used.
However MK kinetic and there are others do switches that send wireless signals, so you can get second two way without wires.
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