My brother has in his dining area a central light and two wall lights.  They 
were operated from just one two gang wall switch, (i.e not 2 way at opposite 
ends of the room).  He wants to change the rocker switch to a 2 gang dimmer. 
He asked me to do it for him and I said I could go over tomorrow night.  I 
told him not to touch anything until I got there.  He has just rung me and 
said her indoors wanted it doing tonight so he stareted it!!!  He wrote down 
the connections and then removed the switch, he took out the new switch (2 
gang 2 way dimmer) and looked for his drawing.  Unable to find it he asked 
wifey if she had seen the "cash machine slip that was on the sideboard", she 
replied "I've shredded it, you're not supposed to leave things like that 
lying around!"

I will go over tomorrow to hopefully sort it but I am not a sparky and 
usually change my light switches etc in the same 'make a drawing' style as 
above.  In the wall back box he has a T&E and a single core grey sheathed 
cable.  The new switchplate has L1, L2 and C on each switch (obviously). 
How do I wire it so that one switch operates the wall lights and one 
operates the central light, everything worked perfectly until he 'forgot' 
where the wires went, so I don't need to lift floorboards etc to get to the 
junction boxes etc.

My thoughts are:
Red to C (then strapped to other C)
Black to L2 (on the same switch as the T&E Red)
Grey single to the other L2.

Is this correct?  If not could somebody help please, I do not want to spend 
all night at my brothers listening to SIL saying "Is it done yet?"

Cheers

John