I do my own heating wiring. But any testing is done by a sparks I know. He also does all my bathroom wiring. I can wire s plans quicker than him so he doesnt mind.
I dabble in a bit of electrics but I've got a contractor I use, there's 2 of them and they are good at heating so I'm happy, saves me couple hours and their cost is factored into the job.
I think you need to define what you mean by electrics. In my experience most self cert electricians would not get involved with wiring heating systems preferring to leave that to the Competent Person or Benchmark certified tradesman. However, since 2005 I have never touched any paying customers electrics especially wet areas, preferring to leave responsibility and verification to a Part P sparks. This followed the successful prosecution and imprisonment of a local kitchen and bathroom installer for doing exactly that.