Electrical – Changing switch to dimmer (UK)

As mentioned in the linked questions (see the above comments) switches that are designed to only work with incandescent bulbs frequently send a low voltage through the bulb when the switch is in the off position. This is to power some component in the switch, like a night light, a motion sensor, or the receiver for a remote control. With newer energy saving bulbs like CFL's and LED's, this low voltage will cause the light to flicker, while it would have gone unnoticed with an incandescent.

The solution is to get a switch that's designed to work with energy efficient bulbs. This switch is either a standard manual switch, or it can have a dedicated neutral connection to send power over for the switch's components. To wire a switch with a dedicated neutral, either the power source needs to go through the switch's junction box, so you can pigtail off the neutral, or if the power source comes from the light fixture, you need a 3 wire connection from the fixture to the switch (hot, switched, neutral).

The loop in the black wire is normal when electricians are running a hot wire from device to device. It saves them time and is really safer since it involves fewer wire nuts.

The orange wire is the wire that is going to the light. The power enters the switch where the black wire is looped over the screw, and exits to the light through the orange wire.

Yes, attach the green wire to the green screw. But, you need to wire the blacks from the switch differently. One switch black is for the incoming power, and the other is for the exiting power. So, one needs to be connected to the same black that is connected to the old switch; and one needs to be connected to the orange.

I would, with the power off at the circuit breaker panel, and after testing to make sure the black at the switch is not hot, cut the existing black to form two separate wires and strip the ends appropriately. Then I would connect one of the black wires from the new switch to these two wires with a wire nut. After that, connect the other black for the new switch to the orange with a wire nut. That should do it, and your dimmer should now work. Good luck, and be careful!

PS: I personally use a Fluke 1AC-A1-II Volt-Alert AC Non-Contact Voltage Tester to verify or locate hot wires and love it. You might want to check it out for the future. Its inexpensive too. Note: I have no personal connection to Fluke; I just think good products like this are worth spreading the word about.