Wiring diagnostics for new light to 2-way 1 light arrangment

[RSE]

Hi Folks - I’m struggling with wiring a new light to an existing 2-way 1-light arrangement (i.e I’m adding a new light at the base of the stairs and want both upstairs and downstairs lights to simultaneously be controlled by the existing two switches). I’ve done sufficient research on YT and Google to confuse myself as to where I’m going wrong or if what doing is unachieveable.

The arrangement has T&E from the existing light running to the existing switch

Red is in L1

Black is L2

I then have 3C&E running from the upstairs switch

Yellow is L1

Blue is L2

Black is Common

running to the downstairs switch

Red is Common

Blue is L1

Yellow is L2

And then 3C&E from the downstairs switch

Red is Common

Grey is L1

Black is L2

feeding to the new light where

Red is Loop

Grey is N

Black is L

Can you call on your expertise to guide me? Thanks

 

[EFLImpudence]

Firstly - just to make sure, would these colours be more accurate?

The arrangement has T&E from the existing light running to the existing switch
Red is in L1
Black is L2

I then have 3C&E running from the upstairs switch
Yellow is L1
Blue is L2
Black RED is Common

running to the downstairs switch
Red is Common
Blue is L1
Yellow is L2

And then 3C&E from the downstairs switch
Red BROWN is Common
Grey is L1
Black is L2

feeding to the new light where
Red BROWN is Loop
Grey is N
Black is L

You seem to have an extra cable:
One from upstairs switch, one to downstairs switch - presumably the same cable but then
one from the downstairs switch - where does this one go?

Then one feeding the light.
AND Where did you get the Neutral from?

 

[RSE]

Thanks for the comments!!

Some clarifying info. Diagram below is the circuit (with the dotted section being added by me).

The first picture is the upstairs switch which shows 3C&E on the left side (which leads to the downstairs switch) and second picture shows the T&E from the upstairs light.

Third picture is the downstairs light switch (the unsheathed Earth has now been sheathed).

 

[terryplumb]

If the current two way switching works fine ,and all you want to do is introduce a second light fitting to that set up ,just run a twin and earth from the existing lights terminals to the new light fittings location.

 

[EFLImpudence]

You can't just connect the Grey wire to the Blue wire and expect it to magically become a Neutral.
The Blue is the switched live according to the rest your diagram - assuming you got that right.
Where did the LOOP come from on your new light?

The cables are BROWN, Black and Grey. At least you could get that right.