Pjo - the only reason you think that replacing your CU was "no more complicated than wiring a plug except on a much bigger scale" is precisely because of your unknown unknowns.
Maybe the new one was better than what was there before, but that's not the point - you don't know if it is good enough, but by doing the work you took on a legal responsibility to ensure that it was good enough, not just better.
Say you had an unroadworthy car, and you carried out ineffective repairs to it. It might well end up better.
But it would still be unroadworthy.
As RF pointed out, you don't know if your RCDs work properly.
You also don't know if you have proper continuity on your ring final cables, you don't know if your main bonding is OK, you don't know if your fault-loop values are low enough for your MCBs to operate properly, you don't know if the insulation of the cables is all OK, you don't know if the polarity of your installation is correct...
If you want to do the best, neatest, safest and professional job you possibly can then you do need to learn and come to understand why all of the things mentioned in this topic are important.
Many thanks for everyone's response.
I don't disagree that in an ideal world, a professional job is the way to go.
I don't doubt for one minute the expertise and competence of you guys posting on here. But at the same time I have seen some very shoddy work by so called professionals.
The trouble is, there is still no real way (except for word of mouth) in finding a decently skilled, with plenty of experience, that charges a reasonable price, tradesman, whether it's an electrician, a plumber or whatever.
I brought my house because it was all I could afford. At the time Part P didn't exist. If I could afford it, then yes, I would have the house gutted, rewired, re plastered, central heating fitted, new floorboards, new ceilings etc, all done by highly skilled professionals. But I cant. I have to do most of the work myself. I have been doing it up gradually since I brought it and still have a long way to go.
There is a difference in what I've done than to your car example though. A car has to be tested every year. If it doesn't pass the MOT then you need to fix it. If I bodge it and it fails the next MOT, I either fix it properly or it fails again.
There's no such thing with my home electrics. I'd willingly pay the price of a MOT for someone to come out and test my electrics but somehow I think it will cost a lot more than that.
I don't have to get my electrics tested each year, I can simply leave them alone and never touch them until they deteriorate to the point of killing someone or starting a fire. I suspect that if they made it law that everyone had to get their electrics tested say every 2 years, a LOT would fail?
From my point of view, my house has modern wiring (also has old dead wiring left under the floor, odd stuff, looks almost like lead?, breaks if you bend/touch it). So it's been rewired at some point. . When I decided to change the CU, I checked all the plug socket wiring (found a couple of loose connections), checked the junction boxes for the lighting in the attic etc and tidied up a few (probably safe, but I like a neat job) and fitted a modern CU unit. It may well not be 100% up to the latest regulations but if it isn't, I doubt very much whether the problem will be with the CU I've fitted, it will be something else. It also no longer has some of the loose connections in the plug sockets that it used to have. Maybe the RCD isn't tripping when it's supposed to (trips quickly enough if I touch neutral and earth), but even if it was part P tested and shown to be faulty, there's nothing to stop the replacement going faulty after I've got the certificate?
I fail to see how my CU can be any more dangerous than what was originally there (again I take on board everything you've said)
I understand your concerns at the same time, I hope you can appreciate my point of view.
I've had a word with a friend whose a spark, he's going to test my electrics when he has some spare time
)
