No power still going to it tuned off at white switch above it
The white switch will need removing to disconnect the cable, the problem is so often when a switch is removed wires pop out, so first you need to isolate the white switch, or at least switch off the line to it.
If I was reasonably sure which MCB/RCBO fed the switch personally I would take a chance and would behave as if the white switch was still live, however I am still taking a risk, as can't be sure switched off, and it is not isolated, as neutral is still connected, and may have the wrong MCB/RCBO so could be live, so safe way is switching off the isolator at the consumer unit, removing white switch, removing the cable to Randell 103 replacing switch and then turning the isolator back on, this may mean resetting clocks, but is the safe method.
It is all well and good saying
Establish the circuit that the isolator is on ,and electrically isolate it ,at the consumer unit / fuse board.
Prove it is dead with test instrument.
However to do that means removing the cover off the consumer unit or removing switch to actually test, which will likely involve more danger than it guards against, although I have seen where an isolator was by-passed, the chances of some one by-passing the line and not the neutral are very slim, so once switched off you will see there is no power to the house, so you are reasonably sure safe to work on.
Technically you should remove the switch and test with a meter of some type, should be one not requiring batteries and with no selector switches, and then it should be tested with a proving unit to ensure the tester is still working, but to gain access to the terminals to test you have already removed the switch, so if live it's a bit late, so yes that is the official method, but more practical to simply switch off the main isolator to the home.
The problem with testing for dead, is it only tests for dead at that moment of time, so if some timer or thermostat switches after testing it can become live. So far simpler to turn off main isolator. Theory is the supply is spiked so should it switch on there is a short circuit to blow a fuse, in practice that is not done with low voltage (50 - 1000 VAC) it is only done with high voltage.
So since not proved dead, I work as if live, unless I can prove dead, now 69 and clearly still alive.
