Correct, if you try and use the earth conductor as a neutral return on any modern UK wiring system that complies with BS7671 (UK wiring regs) you will trip the RCD. An RCD monitors the current flowing out on the live and back on the neutral and trips if there is much of a difference (usually 30 mili-amps which is a very small amount). If you try and wire up using the ground conductor as a substitute for the neutral you will end up with current from the device flowing back to the switchboard bypassing the RCD neutral connection. This will imbalance your lighting circuit which will imediately trip. The method will work if your house doesn't have RCD protection; however, you will have effectively made your earth / ground conductors in your house carry current. This is not a good idea.