I would draw the line in this circumstance, where the work done by a person in their own house, could affect the safety of other users on the same electricity network.
I know something like this is rather rare, but it has happened before.
Trumpy,
Can you elaborate on this? You've got me trying to imagine what kinds of domestic DIY wiring faults could cause problems further back in the system. Provided the main fuse is not bypassed or upgraded (is that where the problem is?), any overloads or short circuits will only affect the consumer side of the fuse. Mixing up earths and phases will again blow local fuses, whereas earths and neutrals mixed will have no effect on the supply as these should already be connected together at the neutral link.
