finding an electrical fault

Possibly, but it could also be a neutral to earth fault. The neutral can become charged if the conductor is in contact with an open live conductor. This can happen through an appliance that has a low enough resistance that allows a high enough current out through the neutral and the neutral side of the appliance has come into contact with the earth conductor. Because of the resistance taking some of the oomph out of the current, it then gives enough charge to give the symptoms you describe.

Yoe say that this fault has only reared it head since doing work on the lighting circuits, so my first thoughts are that you've left something on the circuit you were working on, which is now leaking out through the earth conductor. The best way to find the fault is to place a meter over neutral and earth and see what kind of reading you get. Then switch the circuits off at the consumer unit one by one until you find the circuit that is causing the leak to earth.
If none of the circuit being switched off cure the problem, then you're looking at a leak to earth from the mains supply side of your system.
You may also find that the fault is occuring only when one particular appliance or light is switched on or off, so you would then be able to narrow the fault down to somewhere on that one circuit.

There is no real way of telling if this fault would create enough of anything so you could make a warning system to detect it. Just make sure that all the safety systems installed in appliances, in plug tops and in the consumer unit are all rated correctly for the circuits they control.

Good luck with it.

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