The (early victorian terrace) house was bought by a 'builder' - a proper cowboy I have since discovered - and modernised, it didn't have central heating, he removed chiney breast and took out an internal wall, all looked like it had been done properly - labc letters etc.
But the longer we've been here the more things are starting to fall apart. He must have done most things himself and just got a spark to do the cu change - also did power to detached garage (swa all looks fine) and main bonding. He did everything as cheap as possible as he wasn't going to live in the house himself.
I think the spark just chanced it, no way the builder wouldn have paid for a pir. Problem is, when you chance it you sometimes get caught out. The house must have been rewired around 20 years ago and I think he must have looked at most of it and thought it was all ok, but missed this. This cable fed an unfused spur with all power in the front room on it. It looks like at some point someone fancied a bit of diy and used a bit of old rubber insulated cable they found under the floor boards (loads of rubbish in the floor void) to spur of a socket. Some years later another diyer thought they'd take a spur of this socket and so on...
Either he didn;t test it properly or more likely he got very low reading and knew he wasn'g going to get paid to do any other remedial work so forgot about it.
The cable just crumbled away as soon as I touched it and must have been about a 8m run to the socket.