Fuse number 4

 She says to stop using the light switch by the  entrance to the flat because it has come loose from the wall. This might be dangerous. This fixture has been defective for ten years now. Everyone has become used to it, it was installed by some electrician who did not realise that it was too close to the swing of the door, and that people would catch their hand between the switch and the door. People did, and the switch got dislodged. It has been hanging there, loosly fixed to the wall for ten years.

Now the wife has become aware that it might be dangerous, and the solution is to not touch it.

Agree that it is to be replace, and suggest the flatter light switch with a toggle and a porcelain base bought some years ago at a brocante market in France. The instant smart remark is that it is probably not a two way switch.

It is.

Remove the screws from the old switch, a huge bakelite rotating type switch. Check that the wooden supports for the interior wall are situated to allow for the mounting of the French switch. And then to the fuse box. See that the lights in the hall and those in the bathroom are on the same circuit as the socket in the hall. The socket in the hall to which the internet appliances are attached is on this circuit too. This is interesting but unimportant. Turn off the fuse No 4.

With the help of a workman's light remove the wires from the old switch and trim them to fit the French switch. Hook up the French switch and turn on the fuse No 4. It works perfectly. 

Turn off the fuse No 4.Then work out a way to fix the switch to the wall, which has been damaged by the repeated accidents with the last switch. It had been impossible to open the door and turn on the light at the same time, without catching ones hand between light switch and door.

Finally, find a way and find screws of a suitable length to serve.

Mix up a small amount of plaster to fill the crater left in the wall by the old switch. Fill the crater and smooth the whole thing with a wet smoothing sponge. Then mount the switch as planned.

Turn on the fuse No 4. It works perfectly.