Sometimes you might want more than two switches on a lighting circuit. For example, one switch at each end of a hallway with another at the top of the stairs. If you have a big landing, you might even want four switches! Here’s how you do it.
The third switch is referred to as an Intermediate Switch, although technically speaking it’s a Double-Pole Double-Throw switch. The Brown wire doesn’t connect to the switch, it’ll have to be joined with a connector in the back-box. The Earth will also have to be joined in the back-box, on the Earth bonding point if it’s a metal box. The Grey and Black wires connect to each side of the switch.
If you want more than three switches, just keep adding Intermediate ones in the same manner. They can go on either (or both) the Switch One or Switch Two sides.