What could be causing an earthing fault in a specific socket?
I just had a similar issue. Chances are a wire in the outlet is shorting another wire. You probably can't see it in that outlet because the short is from another outlet. Ie. Where the outlet is fed from. With a multimeter check the outlet and you will likely get strange voltages or as you said full line voltage on the ground. Check the voltage on the steel electrical box itself, it should be zero but it sounds like that will have power which is not good. Now go to the next outlet in the chain / circuit and check the voltages again. Keep going to each outlet in the circuit until you find the issue. To find out which outlets are part of the circuit, turn of the circuit breaker and check power throughout the house. Alternatively you can guess when you remove the outlet and look where the wire is going behind the drywall.