Hi,
Thanks for the comments (I've been away for work and just got back, so catching up.)
I've spoken to the previous owner - he says everything was working OK but just before vacating he had a handyman replace the 3 gang as the previous one was cracked (though working). Workman wasn't a sparks...
I have just got a house with a 3 gang, 2 way light switch which isn’t working properly. The wiring looks dodgy (particularly the connection from 2 COM to 3 COM) but I’m not totally sure where everything should be. Grateful for any ideas. Wiring diagram below: