Landing 2 way wiring problem

[mooney3]

I have a 2 gang 2 way switch at the bottom of the stairs to work the upstairs and downstairs landing lights. I have a single 2 way switch at the top of the stairs to work the upstairs light.
The problem I have is that I can turn the upstairs light on/off from the upstairs switch but not from the downstairs switch. The downstairs light works perfectly well.
The wiring is as follows:
Upstairs 2 way switch. Red to L1, Red to L2 and Black to common.
Downstairs 2 way 2 gang switch. red to L2 and Black to common (left switch for upstairs light) & the same on the right switch for the downstairs light
The ceiling rose at the top of the stairs has a brown from the lamp going to the live connection and a GREY heavy sleeved wire to the same connection.
There is a Blue wire from the lamp going to the Neutral connection and a Black wire going to the same Neutral connection.

I can't see any other cables/wires.

Any help appreciated.

 

[Steve]

Post a few pictures if you can. The way you describe, it would never work. ever.

We need to know what cores go where on the 2 switches, and which ones are singles.

 

[securespark]

I can turn the upstairs light on/off from the upstairs switch but not from the downstairs switch.

You have a problem between the L1's and L2's of the affected switches.