To me this exemplifies the massive flaw with part P in particular, and building regs in general.
If I was getting a "random" electrician from the yellow pages to do some work for me, then buildings regs would be a good 'safety net', but if either I'm doing the work and am competent, or I am confident in the electrician who is doing the work, then buildings regs just gets in the way and adds extra expense, difficulty and trouble.
All it does is encourage people not to do things properly. If I could, for instance, run a new circuit consisting of a 2 metre cable from the CU to a burglar alarm, get a BCO out to have a look, let him have a poke around the installation and show him my test results (and do the tests in front of him if necessary) and pay him £50 there wouldn't be an issue. But, he wants to have two site visits to look at first fix and second fix (for a 2 metre cable run in trunking FFS.. (and why, if he doesn't understand electrics?)) and have me pay £270 for a job that would take 30 minutes and cost <£20 in materials.
A quicker/cheaper check-up would quickly find the people who wire 13A sockets with bell wire (and they could still do that now...) or those who put a new ring in without doing any tests at all. Really that's all that's needed. An installation certificate and a quick visual check should suffice for ANY installer (unless the visual check shows issues).
If a BCO doesn't understand enough electrics to know what's safe and what's not, then they should get BCOs who can! Somehow they know about everything else.
Apparently there were about 10 deaths a year prior to 2005 due to 'electrical faults' in the home. Most of these were probably due to mis-use or faulty appliances. AFAIAA there were no statistics published about how many were due to faulty installations. It would be interesting to know whether this has gone down or up after 2005...