Our issue stemmed from buying our house in the summer i.e. in daylight. One of the lights in the lounge didn't work so after the basic's (bulb - ok, supply to fitting - not ok), I discovered that the wiring (behind the horsehair plaster) was that nice mix of metal conduit, brass fittings and 2 core (live and neutral); you no earth.
I never did find out where the failure was; I ripped the whole lot out, this was pre- Part P/harmonization, and started again.
I suspect that the small sample on incompetence posted in the forum is the reason for Part P. If you take your time rewiring isn't *that* difficult; ok I had oversite from qualified father-in-law particularly with the 2 way lighting but putting the ring circuits in place wasn't that hard. The arse was the prep before and the £300 a wall the replastering cost; every room was wallpapered so big money there..
Talking of kitchen fitters, I don't trust them either as the (Hygena) contractors that did this for the previous owners managed to tile/plaster around the boiler so the cover couldn't be removed if it needed to be serviced. The gas fitter who came to do the service wasn't that impressed and blamed me for being an idiot. Although the brand isn't in the UK these days, depressingly I suspect the sub-contractors that did the fitting are still active.