Ah fantastic, thank you so much for your help. I'll have a go tomorrow when its light. So do I remove the yellow that is being used as the earth? Sorry for all the questions.
It seems strange though that the yellow on both switches has been put onto the back box upstairs and then the switch earth downstairs don't you think? And then as you say Harry I don't do understand why there is a yellow/green earth that has been connected to the switch upstairs?
In the intermediate switch the yellow cable goes to the earth point in the back box, I'm going to open the downstairs switch now and send some pictures.
There isn't three switches, its just the downstairs 2 gang switch and then the upstairs intermediate switch. The photo I have just sent is the intermediate switch.
There is something in L1 though? I read that in order to use an intermediate switch as a 2 way switch you had to have a com, L1, and L2. But I am currently using l1,l2,l3 and l4.