There was one in South Wales, it was over an EICR, and it was because he charged for work not done, not that the work done was sub standard, he pleaded guilty, I think had he fought it, it may have failed.
But as to if rare, not a clue, we only see cases which hit the news.
Be it the Emma Shaw case, or any other, we know there must be loads which simply don't come to court, only when it comes to court, do we know a bit of what when on.
The electricians mate clearly did not have the electrical qualifications required to complete the installation certificate. And to put his name on the certificate was clearly wrong.
However, to plug in a tester, press the button marked test, and to write down what the meter said is not rocket science, and had he done that, it would have likely said something like OL, at which the foreman would have realised there was a fault.
It was the electricians mate talking in the canteen and making up some likely reading when it did not work, that caused the problem to be missed.
The IET forum did have quite a write up at the time, but still some reported facts, are a little vague, mainly down to when things were done, we know a loop of wire was damaged by the plasterer which damaged the earth wire, and that there had been signs of arcing, which tripped the overload, which was then reset, but us the reader has no idea who made it live to start with? As it seems likely there would have been a large bang, which should have alerted there was a fault.
There was so much missing in the report, likely it did come out in court, but we were not told what had happened. Net result was after that we saw very few electricians mates. Firms did not want to take the chance. We are looking back some 20 odd years, the 2008 version of BS 7671 in essence stopped a repeat, with the new rules on RCD use.
more on the case here but it shows how hard it is to work out if someone is qualified, "he had 30 years of practical experience working as an electricians mate, and suggested that there was no way to accurately measure his true ability."