Rpa07, you might be right, "good old all-rounder", fed up with so-called experts in the past. I do plumbing but not gas, I do joinery, and just about everything else, including some electrical work, but I do know my limitations. That's why I enjoy this forum so much as it is a great place to learn. The fact that I like to learn stuff doesn't mean I'm going to do it, just that I like to find out new stuff. Thus, while I am happy doing most jobs, running cable, changing switches and sockets etc I don't even think about holding myself out as an electrician, and installing a CU is a step too far...3 steps too far, because I don't have the equipment or knowledge to test everything. Example: my cloakroom fan has stopped working today. It has been fine for over 10 years, and I installed it in place of one the builder put in that couldn't shift a fart in 2 hours...oh yes, I needed a fan in there due to Building Regs, but he put in the cheapest fan he could find...it was totally ineffective, but it was a fan...so, compliance, apparently. I researched, bought a centrifugal fan with good spec for air changes, and it has been fine.
I have checked this failed fan this afternoon. There is power to the isolator, there is power to the fan connector block, so I simply conclude the fan is duff. I will order a straight-forward replacement and connect it. I don't think that's excessive DIY. Had there been a power supply problem, suggesting a fault upstream of the isolator, ok, I might have had a look, but if there was nothing obvious like a poor connection at a JB, wel...I'd call an electrician in...and just hope he/she wasn't a kitchen fitter masquerading as a spark!