My understanding is that any unapproved person is not allowed to as much as unscrew face plates. I have seen 4inch nails in fuseboards, fuses wrapped in tin foil, whole kitchens wired off single 2.5mm t+e spur, armoured cables for flats running through the wrong flats, etc, etc and I am just a carpenter! They really had to tighten up - it was unbeleivable some of the dodgy electrics I've seen. One of the common faults when changing "like for like" is that untrained people can over/under tighten grub screws or inadvertantly stripping and bridging cable as the re-fix the fitting. I'm just a carpenter and I fully agree with the tightening up of electrical work. I am a stickler for security, electrical and gaswork and general good practice. Each man to their trade as they say.
Steven Diver ● 4663d