A lot of people, particularly those that fancy themselves as Handymen, will have a go at doing things in their own homes. I do my own plumbing and joinery work - I imagine Plumbers and Joiners could have a good moan about that.
Unfortunately, domestic electrical work is seen by the layman as just placing a wire from A to B and sticking a socket or whatever on the end of it. ( How many of us have heard other tradesmen on site saying " I could do electrical work, its easy").
The layman, not being an Electrician, is probably unaware of the dangers of doing his or her own work apart from, of course, the
legendary Belt.
With the price of getting a tradesman in to do the work, it is not surprising that people attempt it themselves. It will always happen and nothing can be done about it.
My advice is don`t worry about it, but do worry about other things like, paying for an ECS card, paying for your 2391, paying for your part P and your membership of the NICEIC or other scheme not forgetting your Public Liability insurance and of course last but not least, the never ending revisions of the good old BS7671.