To be fair to the builder I think he did use an electrician to run the wiring so apologies for giving a bad impression of him. Looks like I need to identify which is the live conductor missing the brown sheath then? I'll get my multi-meter on it! What damage might have been done to the wiring? The switch is probably damaged because I've shorted it so many times now.
Put your multimeter away and phone a spark.
You aren’t competent enough to be dealing with stuff like this. No offence mate