New Dimmer Switch?

I am trying to install a dimmer switch in my friends lounge. The only problem is is that someone stupid has disconnected the wiring from the old switch and I am unsure how to connect the dimmer up. I do know that the old switch which he still has has a small red cable going from Common on one switch to Common on the other. I am left with two lots of cables, red and black in each set. The earth is connected to the box in the wall. Can anyone tell me how I am supposed to connect the L1 and L2 on each dimmer switch with the red and black cables. I think I am supposed to still use the separate red cable to connect common to comon. I have been on the internet and most sites explain blue and yellow cables or black and white cables. I don't have these just Red and Black. Any help anybody can give me would be greatly appreciated.