Slight voltage reaching GU10 LED lamps when switch is off

[alan.surry]

We've replaced a load of GU10 halogen spotlights with 1W LED spotlights in almost every room around the house & have discovered that the a couple of the lights have a slight glow when the switches are in the off position. The upstairs & downstairs lights are each on their own circuits protected by 6a MCB's and the faults are on 1 bedroom (1 way) 1 downstairs room (1 way) & the stairs (2 way). There are other rooms on each circuit that are unaffected.

I'm qualified to C&G 2330 Pt2 & am part way through year 3, so I've got a good understanding of the circuits and a basic knowledge of inspecting & testing, but don't have any professional testing equipment other than a digital multimeter (I'm a network engineer by trade). My gut feeling is that the problem is with the earthing as I've found the earth for the downstairs circuit cut back & disconnected at the consumer unit, presumably by the previous occupiers or their cowboy builders (I've already found 1mm twin & earth on a couple of 13a twin socket spurs whilst renovating!)

Assuming there is a fault in the earthing, is it safe to protect the faulty circuits by installing RCD's, or will it be necessary to replace the wiring? The CCU is a split board proteus model, which I'm told I can get combined MCB/RCD's for. The total load on each circuit will be less than 100 watts when we've finished replacing the 50w halogens with the 1w LED's.

Any advice would be helpful.

Regards, Al.

[Sparky]

there is a good practice guide for reconnecting a lighting circuit with no cpc, the long and short of it is the circuit must be on RCBO and no metal fittings.

We had Similar issue with energy saving lights, at first we thought it was an inductance issue, until we visited the property and found the owner had wired the smoke detector across the line and switching wire of lighting circuit.