So, the vultures gather looking for an easy meal. But from where I'm sat, I can't actually see a dead animal. Not even one with a limp, at the moment.
Come on guys, this is getting stupid. OP suggests a list of work and seems to pay a fair price, list of work done suggests knowledge of what should be installed to meet regs, etc.
Ooh, but a black cable, you cry. So what? Has anyone stopped to ask if it's been surface clipped for some reason? Or stopped to consider that it might have been done as an alternative to needing to fit an RCD even.
Yes, the OP should check the electricians credentials and that he'll be getting the Part P paperwork, but to suggest more than that based purely on syniscm and tutting just gets us ALL a bad name.