......
An 8.5KW shower, wired in 2.5mm˛ T&E, and spurred off the upstairs ring main.....that's when you know you are lucky to be alive.

I've seen photo's of similar DIY gas instalations ie a length of garden hose to extend the gas main! :-?
My favourite was my last house when I bought it.
60's bungalow with the traditional (for the time) single 13A socket in each room, all on a nice ring main.
DPO had wired at least another 8 13A sockets (some double) but, obviously not a fan of ring mains, he had wired each of these radially to a point just above the kitchen, using whatever wire he had hanging around. Here all the wires were rammed into a chocolate block.
These were all fed from the now redundant cooker feed (gas cooker and hob - another horror story for another day). Problem was, he couldn't ram the 6mm
2 T&E into the chocolate block in addition to all the radials so he went down to 1mm
2 for a short length beforehand

.
So, half the sockets in the house, fed via a length of 1mm
2 T&E fused at 30 amps.

He'd also spurred from the immersion heater feed to power the central heating, but had simply twisted the wires together and left them laying in the loft, with no attempt at insulation whatsoever, let alone a junction box.

Oh, and the whole house had no earth connection whatsoever, as he'd disconnected the bonding to the mains water feed (which had a plastic meter housing anyway) and it didn't have PME.
I'm glad I bought that house, because if it had been someone less "au fait" with things electrical someone would have been killed without a doubt.

Kevin